The protein in 5% STCA unfolds completely in urea concentrations greater than 1.8M [Fig. Hydrochloroacetic acid did not precipitate aFGF in the concentration range 090% v/v [Fig. The potency of an acid to precipitate proteins appears to depend not only on the nature of the anion but also on its ability to stabilize the precipitation-competent intermediate(s). The acid(s) treated proteins solutions were incubated at 25C for 1 h. The precipitated proteins samples were pelleted down by centrifugation at 12,000 rpm for 20 min. de Roos B, Duthie SJ, Polley AC, Mulholland F, Bouwman FG, Heim C, Rucklidge GJ, Johnson IT, Mariman EC, Dnaiel H, Elliott RM. Panel (A) Fraction of unfolded species of the aFGF formed at various concentrations of urea. It is important to understand if proteins precipitated by TCA can be completely recovered in solution in their native conformation.
Owing to the high content of arginine and lysine residues in aFGF, we opted to probe the conformational flexibility of the partially structured intermediate state(s) that accumulates in 5% (w/v) STCA. Hongbo X, Slobodan V, Lilia MI, Oldfield CJ, Dunker KA, Uversky VN, Obradovic A. Functional anthology of intrinsic disorder. In summary, these results clearly suggest that the TCA-induced precipitation profiles are independent of the native conformation of proteins. These results show that STCA is a protein denaturant, and the unfolding of aFGF is complete in concentrations of STCA greater than 20% w/v [Fig. Carpentier SC, Witter E, Laukens K, Deckers P, Swennen R, Panis B. Learn more The partially structured state(s) that accumulates in low trichloroacetate concentrations (5% w/v STCA/TCA) closely resembles the acid intermediate (A-state) identified in several proteins.36 The A-states are generally very sticky and show a high-tendency to irreversibly aggregate.36,37 However, in marked contrast, the trichloroacetate-induced precipitate is a reversible association of proteins in their partially structured intermediate state(s). 1H-15N HSQC spectra were recorded at 64 scans at different pH values. Harder A, Wildgruber R, Nawrocki A, Fey SJ, Larser PM, Gorg A. The amino acid residues in aFGF that showed significant chemical shift perturbation and involved in STCA binding are indicated by their single letter codes. Uncovering the unfoldome: enriching cell extracts for unstructured proteins by acid treatment. In general, the TCA-induced protein precipitation curves can be broadly classified in to three different phases. [Fig.4(A)].4(A)]. Partially folded intermediates as critical precursors of light chain amyloid fibrils and amorphous aggregates. Therefore, subtle conformational changes that occur in a protein during equilibrium unfolding/refolding can be easily monitored by the limited proteolytic digestion technique. Panel (C) The percentage of protein present in the supernatant of lysozyme (open circle), aFGF (filled square), carbonic anhydrase (open square), and BSA (open triangle) were measured based on the absorbance at 280 nm. The 308/350 nm emission ratio for aFGF in its native conformation is 4.8 [Fig. Unlike TCA, precipitation of proteins in STCA is not instantaneous.
will also be available for a limited time. Blank corrections were made in all the spectra using 10 mM phosphate buffer containing 100 mM NaCl and respective concentrations of STCA. [Fig.3(B)].3(B)]. Panel (A) Binding of ANS to aFGF at various concentrations of STCA. government site. Panel (A) SDS-PAGE analysis of the TCA-induced precipitation of lysozyme, aFGF, carbonic anhydrase, and BSA. [Fig.1(B,C)].1(B,C)]. Digestion experiments were carried out by independently incubating aFGF in the presence of trypsin in 5% (w/v) STCA (at 1:1 protein to trypsin molar ratio) dissolved in 10 mM phosphate buffer containing 100 mM NaCl. The intensity of this band (after Coomassie Blue Staining) is used as a control to monitor the degree of action of trypsin on the native and the intermediate state(s) of aFGF. Unless specified, all solutions were prepared in 10 mM phosphate buffer (pH 7.0) containing 100 mM NaCl. The products of the protease reaction were analyzed by SDS-PAGE analysis. The site is secure. ; (2) Can TCA precipitate proteins in their unfolded/disordered conformation(s)? Dosztanyi Z, Tompa P. Prediction of protein disorder. [Fig.6(B-b)].6(B-b)]. It is important to mention that such partially unfolded intermediate(s) also accumulate in the STCA-induced unfolding pathway of other proteins, such as lysozyme (Supporting Fig. Panel (A) Fluorescence spectrum of aFGF, (a) extracted in 10 mM tris (pH 7.5), and (b) extracted in 10 mM tris (pH 7.5) containing 500 mM sodium bicarbonate.
Bicarbonate ion possibly appears to reverse the precipitation action of TCA by neutralizing the residual acidic trichoroacetate ions remaining (bound to the protein precipitate) even after extensive washing with acetone. Chi YH, Kumar TKS, Chiu IM, Yu C. Identification of rare partially unfolded states in equilibrium with the native conformation in an all beta-barrel protein. Tricholoacetic acid is the most acidic of the all the choloroacetic acids used. It is not unreasonable to conceive that the observed longer elution times of the aFGF fractions are due to the highly compact nature of the partially unfolded stable intermediate states that accumulate in 5% w/v STCA. [Fig.3(A)].3(A)]. 8600 Rockville Pike In this context, it would be of interest to note that Cortese et al.,31 observed that unstructured proteins in E. coli have a lower tendency to precipitate in TCA. Ingredients for Luria Broth were obtained from AMRESCO. Interestingly, the recovery of the protein in the native conformation significantly increased with the inclusion of sodium bicarbonate in 10 mM tris buffer (pH 7.5). Heparin-sepharose was obtained from Amersham Pharmacia Biotech. Urea-induced equilibrium unfolding of aFGF in 5% w/v STCA was monitored by steady-state fluorescence. The concentration of the protein was estimated based on the extinction coefficient value of the protein at 280 nm. The expressed proteins were purified on a heparin-sepharose affinity column over a NaCl gradient (01.5M). 1H-15N chemical shift perturbation data obtained using NMR spectroscopy indicate that interactions stabilizing the -strands at the N- and C- terminal ends (of aFGF) are disrupted in the trichloroacetate-induced MG-like state. ; and (4) What is the general mechanism underlying TCA-induced protein precipitation? Panel (D) MolMol representation of the structure of aFGF (grey). The flow rate of elution was 1 mL/min. The absence of the preunfolding baseline (in the unfolding curve obtained using relative fluorescence intensity at 350 nm) precludes the accurate estimation of the parameters of unfolding. S1), suggesting that the TCA is less efficient in precipitation proteins in their denatured states. The protease action was stopped by heating the mixture (protein + trypsin) at 90C for 10 min. Subsequently, several other studies suggested that the acidic nature of TCA is important for the conformational changes that trigger protein precipitation.1921 However, the mechanism by which TCA precipitates proteins is not clearly understood.
The flat portion of the curve (Phase 2), observed in the TCA concentration range of 545% w/v, represents the maximum amount of protein precipitated [Fig. Elution of the protein was monitored by its absorbance at 280 nm. Interestingly, the emission intensity of the dye on binding to aFGF in 5% w/v STCA is twice that observed in the native state of the protein (in 0% STCA). The crosspeaks that show significant decrease in their intensities represent the STCA binding sites. S2). The concentration of the protein used was about 0.5 mg/mL. Residues that show significant decrease in intensity and chemical shift perturbation in presence of 5% w/v STCA are depicted in green. These results suggest that the trichloroacetate moiety is important for protein precipitation. Necessary background corrections were made in all spectra. Proteomic methodological recommendations for studies involving human plasma, platelets, and peripheral blood mononuclear cells. Partial unfolding of proteins results in the exposure of solvent-accessible nonpolar surface(s), and which consequently results in intermolecular coalescence of protein molecules leading to their precipitation. The https:// ensures that you are connecting to the
The spectra were processed on a Windows workstation using Xwin-NMR and Sparky softwares.39, National Library of Medicine Profiling the proteome dynamics during the cell of human hepatoma cells. Existence of molten globule-like state. Panel (B)The percentage of TCA-induced protein precipitation of lysozyme (open circle), aFGF (filled square), carbonic anhydrase (open square), and BSA (open triangle) was measured based on the intensity (after Coomassie blue staining) of the bands of the corresponding proteins on the polyacrylamide gel. In addition, the wavelength of maximum emission of the dye shifts by about 10 nm from 506 nm to 496 nm when the protein is treated with 5% w/v STCA. Before [Fig.1(B)].1(B)]. In contrast, the 308350 nm ratio of aFGF extracted in 10 mM tris (pH 7.5) was only about 0.66, suggesting that only 20% of the protein is recovered in the native conformation. Recombinant aFGF was prepared from transformed Escherichia coli BL21(DE3)pLysS. The degree of cleavage was measured by estimating the intensity of the band (on poly-acrylamide gel) corresponding to aFGF at 16 kDa (remaining after trypsin digestion) using a scanning densitometer. All the UV spectrophotometric measurements were carried out on a Hitachi-3300 spectrophotometer. In this context, the protein precipitating action of acids stronger than TCA such as, trifluoroacetic acid, tribromoacetic acid, perchloric acid, and hydrochloric acid were examined. Panel (C) Crosspeak intensity of residues in the 1H-15N HSQC spectrum of aFGF obtained in the presence of 5% w/v STCA. The Lane-1 represents the trypsin digestion products after various time periods of incubation of native aFGF with trypsin. Extrapolation of the observed retention times to the standard plot (obtained using proteins of known molecular weights), reveals that peaks with retention times of 37 min and 42 min possibly correspond to dimeric and trimeric forms of aFGF, respectively. In general, the decrease in cross-peak intensity of selective residues is ascribed to faster internal mobilities of residues in the flexible regions of the protein molecule. Increase in the TCA concentration(s), beyond 45% w/v (Phase 3), results in a sharp decrease in the amount of protein precipitated, and practically very little or no precipitate is observed beyond 60% w/v TCA [Fig. The unfolding profile shows that protein unfolds completely at urea concentrations greater than 2.8M [Fig. [Fig.55(B)]. In this study, we address these questions using aFGF as a model protein, and attempt to provide a comprehensive understanding of the molecular mechanism underlying the action of TCA on proteins. The results of the study clearly demonstrate that TCA-induced protein precipitation occurs due to the reversible association of the MG-like partially structured intermediate state(s). Denaturation studies on bovine pancreatic ribonuclease. Panel (C) Urea-induced equilibrium unfolding profile of aFGF, native state (filled circle) and in MG- like state in 5% w/v of STCA (open circle). The purity of the protein was assessed using SDS-PAGE. Panel (B) Size exclusion chromatography of aFGF, (a) in the native conformation (0% STCA), (b) in the denatured state(s) in 50% w/v STCA, and (c) in the MG-like state in 5% w/v STCA. The extent of 15N labeling was verified by ES-Mass analysis. Li X, Xu S, Pan C, Zhou H, Jiang X, Zhang Y, Ye M, Zou H. Enrichment of peptides from plasma for peptidome analysis using multiwalled carbon nanotubes. In addition, thermally unfolded aFGF also showed a decreased tendency to precipitate in TCA suggesting that the lower amounts of protein precipitation observed in 6M urea is not due to the interference of the denaturant in the TCA-induced precipitation reaction (data not shown). [Fig.2(A)].2(A)]. [Fig.8(C)].8(C)]. Cross-peaks of some other residues corresponding to Leu28, Tyr29, Val45, Ser72, Meth81, Leu98, Lys115, Trp121, Lys126, Lys132, Gln141, Ala143, Ile144, Leu145, Phe146, Lys148, and Leu149 show significant 1H-15N chemical shift perturbation [Fig. Panel (B) 1H-15N chemical shift perturbation of residues in aFGF in the presence of 5% w/v STCA. Panel (A) shows the far- UV CD spectra of aFGF at different concentrations of STCA. [Fig.2(A),2(A), inset].29 The fluorescence of the lone tryptophan is quenched by the presence of positively charged residues at close proximity in the native structure of aFGF.30 This quenching effect is relieved in the denatured state of aFGF, and the typical tryptophan fluorescence at 350 nm is observed [Fig. [Fig.1AC)].1AC)]. In addition, TCA appears to be less effective in precipitating proteins in the disordered/unfolded state(s). A protein extraction method compatible with proteomic analysis for the euhalophyte. The ellipticity band intensity (at 228 nm) progressively decreases with the increase in STCA concentration, suggesting progressive unfolding of the protein. Peaks representing the native (elution time, 85 0.5 min) and denatured states (elution time, 48 0.5 min) of aFGF were not observed in the elution profile obtained at 5% (w/v) STCA [Fig. In the 1960s, Charles Tanford18 proposed that TCA forces protein to precipitate by sequestering the protein-bound water. Bethesda, MD 20894, Web Policies The secondary structural elements in aFGF include 12 beta strands arranged into a -trefoil motif. Received 2008 Sep 22; Revised 2009 Feb 23; Accepted 2009 Feb 25. protein precipitation, NMR spectroscopy, molten globule-like state(s), protein isolation, proteomics, fibroblast growth factors. Trifluoroacetic acid (TFA), trobromoacetic acid (TBA), and perchloric acid (PA) precipitated aFGF. Da Cruz S, Martinou JC. [Fig.6(B-a)].6(B-a)]. Rajalingam D, Graziani I, Prudovsky I, Yu C, Kumar TKS. (a) 0% w/v STCA, (b) 5% w/v STCA, and (c) 50% w/v STCA.
In this context, we examined the precipitation effects of TCA on aFGF dissolved in 6M urea [Fig. and transmitted securely. In our opinion, the mechanism proposed in this study will provide valuable clues for the development of efficient protocols to capture the entire proteome. The results of the ANS binding and the SEC experiments analyzed in conjunction, clearly suggest that a MG-like intermediate state(s) maximally accumulates in 5% (w/v) STCA. (a) 0% w/v STCA, (b) 5% w/v STCA, and (c) 50% w/v STCA. As mentioned earlier, STCA mimics the protein precipitation action of TCA. TCA-induced protein precipitation curves are U-shaped and the shape of the curve is observed to be independent of the physicochemical properties of proteins. Results of this study clearly demonstrate that TCA-induced protein precipitation is independent of the size and nature of proteins. For the unfolding experiments, protein samples were dissolved in appropriate concentrations of urea prepared in 10 mM phosphate buffer (pH 7.0) containing 100 mM NaCl. Schulman BA, Kim PS, Dobson CM, Redfield C. A residue-specific NMR view of the non-cooperative unfolding of a molten globule. Further increase in the STCA concentration not only results in a progressive decrease in ANS intensity at 520 nm but also is accompanied by a continuous red shift in the wavelength of maximum emission of the dye. Lane M shows the molecular weight marker. Effect of trichloroacetic acid. Panel (A) SDS-PAGE analysis of the precipitate of aFGF formed in different acids. Trichloroacetic acid-induced unfolding of bovine pancreatic ribonuclease. In this context, it should be of interest to note that anions have been shown to exhibit significantly different effects on A-state stability.31. [Fig.2(A),2(A), inset]. The Results of the 1-anilino-8-napthalene sulfonate (ANS) and size-exclusion chromatography, obtained using acidic fibroblast growth factor (aFGF), show that a stable molten globule-like partially structured intermediate accumulates maximally in 5% (w/v) of trichloroacetate. Sample extraction techniques for enhanced proteomic analysis of plant tissues. Wang L, Kallenbach NR. aFGF exhibits weak binding affinity to the dye in its unfolded state(s) in STCA concentrations greater than 20% w/v [Fig. Sample preparation for proteomic analysis involves precipitation of protein using 2,2,2-trichloroacetic acid (TCA). As expected, the precipitation profiles obtained based on absorbance (at 280 nm), of protein(s) remaining in solution, (after TCA precipitation) are U-shaped [Fig. Lane: M, Marker; 1, 0% w/v TCA; 2, 5% w/v TCA; 3, 10% w/v TCA; 4, 15% w/v TCA; 5, 20% w/v TCA; 6, 25% w/v TCA; 7, 30% w/v TCA; 8, 35% w/v TCA; 9, 40% w/v TCA; 10, 45% w/v TCA; 11, 50% w/v TCA; 12, 55% w/v TCA; 13, 60% w/v TCA; 14, 65% w/v TCA; 15, 70% w/v TCA; 16, 75% w/v TCA; 17, 80% w/v TCA; 18, 85% w/v TCA; and 19, 90% w/v TCA, respectively. Fluorescence spectra were acquired using an excitation wavelength of 390 nm and an emission wavelength of 400600 nm. Far UV circular dichroism (CD) spectrum of aFGF in its native conformation shows a strong positive ellipticity band (between 225 and 230 nm) typical of -barrel proteins [Fig. [Fig.2(C)].2(C)]. Protein Science : A Publication of the Protein Society, sodium dodecyl sulfate polyacrylamide gel electrophoresis. Recent studies show that a significant percentage of proteins in the eukaryotic proteome are intrinsically disordered.22,23 It is believed that presence of high proportion of unstructured/disordered proteins in eukaryotes is related to the increased prevalence of signaling and regulation coupled with the fact that signaling functions are enriched in disorder.24 Typically, intrinsically disordered proteins exhibit high-solubility even under extreme conditions due to the presence of large proportion of charged residues and extended backbone structure.25,26 In this background, it will be interesting to examine the effectiveness of TCA to precipitate proteins in their completely denatured state(s). In the absence of STCA, 40% of the band corresponding to undigested aFGF remains after 10 min of incubation with trypsin [Fig. [Fig.6(B-c)].6(B-c)]. S2). [Fig.7(A,B)].7(A,B)]. PMC legacy view Panel (B) Percentage of the 16 kDa aFGF band remaining after incubation with trypsin for various intervals of time.
official website and that any information you provide is encrypted Radivojac P, Iakoucheva LM, Oldfield CJ, Obradovic A, Uversky VN, Dunker AK. [Fig.2(A)].2(A)]. Comparison of yeast cell protein solubilization procedures for two-dimensional electrophoresis. All other chemicals used were of high-quality analytical grade. However, the maximum amount of protein precipitated in TFA was significantly lower than that observed using TCA [Fig.
The HSQC spectra of aFGF acquired beyond 10% w/v STCA show limited chemical shift dispersion and are typical of denatured states of proteins (date not shown). Minimal changes in the ellipticity occur beyond 20% STCA, and the far UV CD spectrum of aFGF in 50% w/v STCA is reminiscent of random coil conformation [Fig. [Fig.5(A)].5(A)]. The amount of protein precipitate formed in different concentrations of TCA (090% w/v) was monitored using SDS-PAGE and by measuring protein absorbance at 280 nm [Fig. These results clearly suggest that the acid nature of TCA does not solely contribute to its protein precipitation property [Fig. [Fig.7(A)].7(A)]. Protein samples were prepared in 10 mM phosphate containing 100 mM NaCl. Urea-induced equilibrium unfolding of aFGF, monitored by changes in the intrinsic tryptophan florescence, shows that the majority of the protein exists in the native conformation at denaturant (urea) concentrations lower than 1M [Fig. Panel (A) SDS-PAGE analysis of the limited trypsin digestion products of aFGF in the native and in the MG- like state(s) in 5% w/v STCA. The shapes of the protein precipitation curves do not seem to be dependent on the physico-chemical properties of the proteins. Wang X, Li X, Deng X, Han H, Shi W, Li Y. Groen AJ, de Vries SC, Lilley KS. The slow precipitation of proteins and the near-neutral nature of STCA provides an avenue to probe the structural transitions that precede the precipitation of proteins induced by TCA. Two closely eluting peaks at 61 min and 64 min were observed in 5% w/v STCA. At low concentrations, the negatively charged tricholoroacetate ions plausibly trigger protein unfolding by disrupting the electrostatic interactions that stabilize the native conformation of proteins. Panel (C) The percentage of protein precipitated in the presence of different concentrations of urea, 0M urea- closed circle, 6M urea- open circle, was measured based on the intensity (after Coomassie blue staining) of the 16 kDa protein band (on the polyacrylamide gel). The new PMC design is here!
Hsieh SY, Zhuang FH, Wu YT, Chen JK, Lee YL. It is believed that the high prevalence of disordered proteins in eukaryotes is related to intense signaling and regulatory activities take place in these organisms.24 Analyses of proteomes generally involve TCA-precipitation prior to detection of proteins on 2D gels. All experiments were performed at 25C. Many cross-peaks show significant chemical shift perturbation and some disappeared in the 1H-15N HSQC spectrum of the aFGF acquired in 5% w/v STCA [Fig. [Fig.1(B)].1(B)]. Biological processes and functions of proteins with long disordered regions. Genomic knowledge has vastly increased with advent of sophistication in methods used in proteomic analysis.13 Two-dimensional gel electrophoresis is the most powerful technique that is routinely used for protein separation and downstream proteomic analysis.4 One of the critical factors governing the success of proteomic analysis is the quality of the sample, which in turn is dependent on the protein extraction protocol(s) used.5,6 An ideal protein extraction procedure should reproducibly trap the most comprehensive repertoire of proteins possible with no or very minimal degradation and contamination by nonproteinaceous compounds.7,8 This is a daunting task because proteins not only have wide array of physicochemical properties like size, charge, hydrophobicity, but also show significant difference in their subcellular localization.9,10 In this background, it is a challenging task to design a generic extraction method to analyze the entire proteome. The lower stability of the STCA-induced MG-like intermediate is consistent with the loss of native tertiary structural interactions in the partially structured state. The intensity of the bands corresponding to the untreated aFGF was considered as a control for 100% protection against trypsin action. 1-anilino-8-naphthalene-sulfonate (ANS) binding experiments at various percentage of STCA (w/v) were performed using a Hitachi F-2500 spectrofluorimeter at 25C. To examine this aspect, aFGF precipitated using 30% w/v TCA was redissolved in 10 mM tris buffer (pH 7.5) containing different concentrations of sodium bicarbonate. [Fig.6(B-c)].6(B-c)]. The expression host strain E. coli BL21(DE3)pLysS is a vitamin B1-deficient host and hence the medium was supplemented with thiamine (vitamin B1). The proteins, aFGF, and lysozyme were treated with TCA and other acids using the method of Sagar et al.38 Protein solutions containing appropriate concentrations of the respective acids were prepared by the addition of requisite amounts of the stock solutions of the individual acids to aqueous solutions of proteins. The inset shows the emission spectra of the aFGF in native (continuous line) and denatured (dotted line) in 6M urea. All gel filtration experiments were carried out at various pH (at 25C) on a superdex-75 column using an AKTA FPLC device (Amersham Pharmacia Biotech). These results clearly demonstrate that unfolding of aFGF in STCA proceeds with the accumulation of an intermediate state(s) resembling the molten globule (MG). Size-exclusion chromatography (SEC) is a valuable technique to obtain information on the conformational changes that occur during the unfolding of proteins.32 SEC is an inert technique and is not known to perturb the equilibrium between the native, intermediate, and denatured states of proteins.32 In this context, the relative population of the various conformational states of aFGF, that may exist under various STCA concentrations, were monitored by SEC. To realize maximal expression yields, the composition of the M9 medium was modified by the addition of a mixture of vitamins. Sivaraman T, Kumar TKS, Jayaraman G, Yu C. The mechanism of 2,2,2-trichloroacetic acid-induced protein precipitation. S1-panel D). Trichloroacetic acid-induced molten globule state of aminoacylase from pig kidney. Results and reliability of protein quantification for two-dimensional gel electrophoresis strongly depend on the type of protein sample and the method employed.
Owing to the high content of arginine and lysine residues in aFGF, we opted to probe the conformational flexibility of the partially structured intermediate state(s) that accumulates in 5% (w/v) STCA. Hongbo X, Slobodan V, Lilia MI, Oldfield CJ, Dunker KA, Uversky VN, Obradovic A. Functional anthology of intrinsic disorder. In summary, these results clearly suggest that the TCA-induced precipitation profiles are independent of the native conformation of proteins. These results show that STCA is a protein denaturant, and the unfolding of aFGF is complete in concentrations of STCA greater than 20% w/v [Fig. Carpentier SC, Witter E, Laukens K, Deckers P, Swennen R, Panis B. Learn more The partially structured state(s) that accumulates in low trichloroacetate concentrations (5% w/v STCA/TCA) closely resembles the acid intermediate (A-state) identified in several proteins.36 The A-states are generally very sticky and show a high-tendency to irreversibly aggregate.36,37 However, in marked contrast, the trichloroacetate-induced precipitate is a reversible association of proteins in their partially structured intermediate state(s). 1H-15N HSQC spectra were recorded at 64 scans at different pH values. Harder A, Wildgruber R, Nawrocki A, Fey SJ, Larser PM, Gorg A. The amino acid residues in aFGF that showed significant chemical shift perturbation and involved in STCA binding are indicated by their single letter codes. Uncovering the unfoldome: enriching cell extracts for unstructured proteins by acid treatment. In general, the TCA-induced protein precipitation curves can be broadly classified in to three different phases. [Fig.4(A)].4(A)]. Partially folded intermediates as critical precursors of light chain amyloid fibrils and amorphous aggregates. Therefore, subtle conformational changes that occur in a protein during equilibrium unfolding/refolding can be easily monitored by the limited proteolytic digestion technique. Panel (C) The percentage of protein present in the supernatant of lysozyme (open circle), aFGF (filled square), carbonic anhydrase (open square), and BSA (open triangle) were measured based on the absorbance at 280 nm. The 308/350 nm emission ratio for aFGF in its native conformation is 4.8 [Fig. Unlike TCA, precipitation of proteins in STCA is not instantaneous.
will also be available for a limited time. Blank corrections were made in all the spectra using 10 mM phosphate buffer containing 100 mM NaCl and respective concentrations of STCA. [Fig.3(B)].3(B)]. Panel (A) Binding of ANS to aFGF at various concentrations of STCA. government site. Panel (A) SDS-PAGE analysis of the TCA-induced precipitation of lysozyme, aFGF, carbonic anhydrase, and BSA. [Fig.1(B,C)].1(B,C)]. Digestion experiments were carried out by independently incubating aFGF in the presence of trypsin in 5% (w/v) STCA (at 1:1 protein to trypsin molar ratio) dissolved in 10 mM phosphate buffer containing 100 mM NaCl. The intensity of this band (after Coomassie Blue Staining) is used as a control to monitor the degree of action of trypsin on the native and the intermediate state(s) of aFGF. Unless specified, all solutions were prepared in 10 mM phosphate buffer (pH 7.0) containing 100 mM NaCl. The products of the protease reaction were analyzed by SDS-PAGE analysis. The site is secure. ; (2) Can TCA precipitate proteins in their unfolded/disordered conformation(s)? Dosztanyi Z, Tompa P. Prediction of protein disorder. [Fig.6(B-b)].6(B-b)]. It is important to mention that such partially unfolded intermediate(s) also accumulate in the STCA-induced unfolding pathway of other proteins, such as lysozyme (Supporting Fig. Panel (A) Fluorescence spectrum of aFGF, (a) extracted in 10 mM tris (pH 7.5), and (b) extracted in 10 mM tris (pH 7.5) containing 500 mM sodium bicarbonate.
Bicarbonate ion possibly appears to reverse the precipitation action of TCA by neutralizing the residual acidic trichoroacetate ions remaining (bound to the protein precipitate) even after extensive washing with acetone. Chi YH, Kumar TKS, Chiu IM, Yu C. Identification of rare partially unfolded states in equilibrium with the native conformation in an all beta-barrel protein. Tricholoacetic acid is the most acidic of the all the choloroacetic acids used. It is not unreasonable to conceive that the observed longer elution times of the aFGF fractions are due to the highly compact nature of the partially unfolded stable intermediate states that accumulate in 5% w/v STCA. [Fig.3(A)].3(A)]. 8600 Rockville Pike In this context, it would be of interest to note that Cortese et al.,31 observed that unstructured proteins in E. coli have a lower tendency to precipitate in TCA. Ingredients for Luria Broth were obtained from AMRESCO. Interestingly, the recovery of the protein in the native conformation significantly increased with the inclusion of sodium bicarbonate in 10 mM tris buffer (pH 7.5). Heparin-sepharose was obtained from Amersham Pharmacia Biotech. Urea-induced equilibrium unfolding of aFGF in 5% w/v STCA was monitored by steady-state fluorescence. The concentration of the protein was estimated based on the extinction coefficient value of the protein at 280 nm. The expressed proteins were purified on a heparin-sepharose affinity column over a NaCl gradient (01.5M). 1H-15N chemical shift perturbation data obtained using NMR spectroscopy indicate that interactions stabilizing the -strands at the N- and C- terminal ends (of aFGF) are disrupted in the trichloroacetate-induced MG-like state. ; and (4) What is the general mechanism underlying TCA-induced protein precipitation? Panel (D) MolMol representation of the structure of aFGF (grey). The flow rate of elution was 1 mL/min. The absence of the preunfolding baseline (in the unfolding curve obtained using relative fluorescence intensity at 350 nm) precludes the accurate estimation of the parameters of unfolding. S1), suggesting that the TCA is less efficient in precipitation proteins in their denatured states. The protease action was stopped by heating the mixture (protein + trypsin) at 90C for 10 min. Subsequently, several other studies suggested that the acidic nature of TCA is important for the conformational changes that trigger protein precipitation.1921 However, the mechanism by which TCA precipitates proteins is not clearly understood.
The flat portion of the curve (Phase 2), observed in the TCA concentration range of 545% w/v, represents the maximum amount of protein precipitated [Fig. Elution of the protein was monitored by its absorbance at 280 nm. Interestingly, the emission intensity of the dye on binding to aFGF in 5% w/v STCA is twice that observed in the native state of the protein (in 0% STCA). The crosspeaks that show significant decrease in their intensities represent the STCA binding sites. S2). The concentration of the protein used was about 0.5 mg/mL. Residues that show significant decrease in intensity and chemical shift perturbation in presence of 5% w/v STCA are depicted in green. These results suggest that the trichloroacetate moiety is important for protein precipitation. Necessary background corrections were made in all spectra. Proteomic methodological recommendations for studies involving human plasma, platelets, and peripheral blood mononuclear cells. Partial unfolding of proteins results in the exposure of solvent-accessible nonpolar surface(s), and which consequently results in intermolecular coalescence of protein molecules leading to their precipitation. The https:// ensures that you are connecting to the
The spectra were processed on a Windows workstation using Xwin-NMR and Sparky softwares.39, National Library of Medicine Profiling the proteome dynamics during the cell of human hepatoma cells. Existence of molten globule-like state. Panel (B)The percentage of TCA-induced protein precipitation of lysozyme (open circle), aFGF (filled square), carbonic anhydrase (open square), and BSA (open triangle) was measured based on the intensity (after Coomassie blue staining) of the bands of the corresponding proteins on the polyacrylamide gel. In addition, the wavelength of maximum emission of the dye shifts by about 10 nm from 506 nm to 496 nm when the protein is treated with 5% w/v STCA. Before [Fig.1(B)].1(B)]. In contrast, the 308350 nm ratio of aFGF extracted in 10 mM tris (pH 7.5) was only about 0.66, suggesting that only 20% of the protein is recovered in the native conformation. Recombinant aFGF was prepared from transformed Escherichia coli BL21(DE3)pLysS. The degree of cleavage was measured by estimating the intensity of the band (on poly-acrylamide gel) corresponding to aFGF at 16 kDa (remaining after trypsin digestion) using a scanning densitometer. All the UV spectrophotometric measurements were carried out on a Hitachi-3300 spectrophotometer. In this context, the protein precipitating action of acids stronger than TCA such as, trifluoroacetic acid, tribromoacetic acid, perchloric acid, and hydrochloric acid were examined. Panel (C) Crosspeak intensity of residues in the 1H-15N HSQC spectrum of aFGF obtained in the presence of 5% w/v STCA. The Lane-1 represents the trypsin digestion products after various time periods of incubation of native aFGF with trypsin. Extrapolation of the observed retention times to the standard plot (obtained using proteins of known molecular weights), reveals that peaks with retention times of 37 min and 42 min possibly correspond to dimeric and trimeric forms of aFGF, respectively. In general, the decrease in cross-peak intensity of selective residues is ascribed to faster internal mobilities of residues in the flexible regions of the protein molecule. Increase in the TCA concentration(s), beyond 45% w/v (Phase 3), results in a sharp decrease in the amount of protein precipitated, and practically very little or no precipitate is observed beyond 60% w/v TCA [Fig. The unfolding profile shows that protein unfolds completely at urea concentrations greater than 2.8M [Fig. [Fig.55(B)]. In this study, we address these questions using aFGF as a model protein, and attempt to provide a comprehensive understanding of the molecular mechanism underlying the action of TCA on proteins. The results of the study clearly demonstrate that TCA-induced protein precipitation occurs due to the reversible association of the MG-like partially structured intermediate state(s). Denaturation studies on bovine pancreatic ribonuclease. Panel (C) Urea-induced equilibrium unfolding profile of aFGF, native state (filled circle) and in MG- like state in 5% w/v of STCA (open circle). The purity of the protein was assessed using SDS-PAGE. Panel (B) Size exclusion chromatography of aFGF, (a) in the native conformation (0% STCA), (b) in the denatured state(s) in 50% w/v STCA, and (c) in the MG-like state in 5% w/v STCA. The extent of 15N labeling was verified by ES-Mass analysis. Li X, Xu S, Pan C, Zhou H, Jiang X, Zhang Y, Ye M, Zou H. Enrichment of peptides from plasma for peptidome analysis using multiwalled carbon nanotubes. In addition, thermally unfolded aFGF also showed a decreased tendency to precipitate in TCA suggesting that the lower amounts of protein precipitation observed in 6M urea is not due to the interference of the denaturant in the TCA-induced precipitation reaction (data not shown). [Fig.2(A)].2(A)]. [Fig.8(C)].8(C)]. Cross-peaks of some other residues corresponding to Leu28, Tyr29, Val45, Ser72, Meth81, Leu98, Lys115, Trp121, Lys126, Lys132, Gln141, Ala143, Ile144, Leu145, Phe146, Lys148, and Leu149 show significant 1H-15N chemical shift perturbation [Fig. Panel (B) 1H-15N chemical shift perturbation of residues in aFGF in the presence of 5% w/v STCA. Panel (A) shows the far- UV CD spectra of aFGF at different concentrations of STCA. [Fig.2(A),2(A), inset].29 The fluorescence of the lone tryptophan is quenched by the presence of positively charged residues at close proximity in the native structure of aFGF.30 This quenching effect is relieved in the denatured state of aFGF, and the typical tryptophan fluorescence at 350 nm is observed [Fig. [Fig.1AC)].1AC)]. In addition, TCA appears to be less effective in precipitating proteins in the disordered/unfolded state(s). A protein extraction method compatible with proteomic analysis for the euhalophyte. The ellipticity band intensity (at 228 nm) progressively decreases with the increase in STCA concentration, suggesting progressive unfolding of the protein. Peaks representing the native (elution time, 85 0.5 min) and denatured states (elution time, 48 0.5 min) of aFGF were not observed in the elution profile obtained at 5% (w/v) STCA [Fig. In the 1960s, Charles Tanford18 proposed that TCA forces protein to precipitate by sequestering the protein-bound water. Bethesda, MD 20894, Web Policies The secondary structural elements in aFGF include 12 beta strands arranged into a -trefoil motif. Received 2008 Sep 22; Revised 2009 Feb 23; Accepted 2009 Feb 25. protein precipitation, NMR spectroscopy, molten globule-like state(s), protein isolation, proteomics, fibroblast growth factors. Trifluoroacetic acid (TFA), trobromoacetic acid (TBA), and perchloric acid (PA) precipitated aFGF. Da Cruz S, Martinou JC. [Fig.6(B-a)].6(B-a)]. Rajalingam D, Graziani I, Prudovsky I, Yu C, Kumar TKS. (a) 0% w/v STCA, (b) 5% w/v STCA, and (c) 50% w/v STCA.
In this context, we examined the precipitation effects of TCA on aFGF dissolved in 6M urea [Fig. and transmitted securely. In our opinion, the mechanism proposed in this study will provide valuable clues for the development of efficient protocols to capture the entire proteome. The results of the ANS binding and the SEC experiments analyzed in conjunction, clearly suggest that a MG-like intermediate state(s) maximally accumulates in 5% (w/v) STCA. (a) 0% w/v STCA, (b) 5% w/v STCA, and (c) 50% w/v STCA. As mentioned earlier, STCA mimics the protein precipitation action of TCA. TCA-induced protein precipitation curves are U-shaped and the shape of the curve is observed to be independent of the physicochemical properties of proteins. Results of this study clearly demonstrate that TCA-induced protein precipitation is independent of the size and nature of proteins. For the unfolding experiments, protein samples were dissolved in appropriate concentrations of urea prepared in 10 mM phosphate buffer (pH 7.0) containing 100 mM NaCl. Schulman BA, Kim PS, Dobson CM, Redfield C. A residue-specific NMR view of the non-cooperative unfolding of a molten globule. Further increase in the STCA concentration not only results in a progressive decrease in ANS intensity at 520 nm but also is accompanied by a continuous red shift in the wavelength of maximum emission of the dye. Lane M shows the molecular weight marker. Effect of trichloroacetic acid. Panel (A) SDS-PAGE analysis of the precipitate of aFGF formed in different acids. Trichloroacetic acid-induced unfolding of bovine pancreatic ribonuclease. In this context, it should be of interest to note that anions have been shown to exhibit significantly different effects on A-state stability.31. [Fig.2(A),2(A), inset]. The Results of the 1-anilino-8-napthalene sulfonate (ANS) and size-exclusion chromatography, obtained using acidic fibroblast growth factor (aFGF), show that a stable molten globule-like partially structured intermediate accumulates maximally in 5% (w/v) of trichloroacetate. Sample extraction techniques for enhanced proteomic analysis of plant tissues. Wang L, Kallenbach NR. aFGF exhibits weak binding affinity to the dye in its unfolded state(s) in STCA concentrations greater than 20% w/v [Fig. Sample preparation for proteomic analysis involves precipitation of protein using 2,2,2-trichloroacetic acid (TCA). As expected, the precipitation profiles obtained based on absorbance (at 280 nm), of protein(s) remaining in solution, (after TCA precipitation) are U-shaped [Fig. Lane: M, Marker; 1, 0% w/v TCA; 2, 5% w/v TCA; 3, 10% w/v TCA; 4, 15% w/v TCA; 5, 20% w/v TCA; 6, 25% w/v TCA; 7, 30% w/v TCA; 8, 35% w/v TCA; 9, 40% w/v TCA; 10, 45% w/v TCA; 11, 50% w/v TCA; 12, 55% w/v TCA; 13, 60% w/v TCA; 14, 65% w/v TCA; 15, 70% w/v TCA; 16, 75% w/v TCA; 17, 80% w/v TCA; 18, 85% w/v TCA; and 19, 90% w/v TCA, respectively. Fluorescence spectra were acquired using an excitation wavelength of 390 nm and an emission wavelength of 400600 nm. Far UV circular dichroism (CD) spectrum of aFGF in its native conformation shows a strong positive ellipticity band (between 225 and 230 nm) typical of -barrel proteins [Fig. [Fig.2(C)].2(C)]. Protein Science : A Publication of the Protein Society, sodium dodecyl sulfate polyacrylamide gel electrophoresis. Recent studies show that a significant percentage of proteins in the eukaryotic proteome are intrinsically disordered.22,23 It is believed that presence of high proportion of unstructured/disordered proteins in eukaryotes is related to the increased prevalence of signaling and regulation coupled with the fact that signaling functions are enriched in disorder.24 Typically, intrinsically disordered proteins exhibit high-solubility even under extreme conditions due to the presence of large proportion of charged residues and extended backbone structure.25,26 In this background, it will be interesting to examine the effectiveness of TCA to precipitate proteins in their completely denatured state(s). In the absence of STCA, 40% of the band corresponding to undigested aFGF remains after 10 min of incubation with trypsin [Fig. [Fig.6(B-c)].6(B-c)]. S2). [Fig.7(A,B)].7(A,B)]. PMC legacy view Panel (B) Percentage of the 16 kDa aFGF band remaining after incubation with trypsin for various intervals of time.
official website and that any information you provide is encrypted Radivojac P, Iakoucheva LM, Oldfield CJ, Obradovic A, Uversky VN, Dunker AK. [Fig.2(A)].2(A)]. Comparison of yeast cell protein solubilization procedures for two-dimensional electrophoresis. All other chemicals used were of high-quality analytical grade. However, the maximum amount of protein precipitated in TFA was significantly lower than that observed using TCA [Fig.
The HSQC spectra of aFGF acquired beyond 10% w/v STCA show limited chemical shift dispersion and are typical of denatured states of proteins (date not shown). Minimal changes in the ellipticity occur beyond 20% STCA, and the far UV CD spectrum of aFGF in 50% w/v STCA is reminiscent of random coil conformation [Fig. [Fig.5(A)].5(A)]. The amount of protein precipitate formed in different concentrations of TCA (090% w/v) was monitored using SDS-PAGE and by measuring protein absorbance at 280 nm [Fig. These results clearly suggest that the acid nature of TCA does not solely contribute to its protein precipitation property [Fig. [Fig.7(A)].7(A)]. Protein samples were prepared in 10 mM phosphate containing 100 mM NaCl. Urea-induced equilibrium unfolding of aFGF, monitored by changes in the intrinsic tryptophan florescence, shows that the majority of the protein exists in the native conformation at denaturant (urea) concentrations lower than 1M [Fig. Panel (A) SDS-PAGE analysis of the limited trypsin digestion products of aFGF in the native and in the MG- like state(s) in 5% w/v STCA. The shapes of the protein precipitation curves do not seem to be dependent on the physico-chemical properties of the proteins. Wang X, Li X, Deng X, Han H, Shi W, Li Y. Groen AJ, de Vries SC, Lilley KS. The slow precipitation of proteins and the near-neutral nature of STCA provides an avenue to probe the structural transitions that precede the precipitation of proteins induced by TCA. Two closely eluting peaks at 61 min and 64 min were observed in 5% w/v STCA. At low concentrations, the negatively charged tricholoroacetate ions plausibly trigger protein unfolding by disrupting the electrostatic interactions that stabilize the native conformation of proteins. Panel (C) The percentage of protein precipitated in the presence of different concentrations of urea, 0M urea- closed circle, 6M urea- open circle, was measured based on the intensity (after Coomassie blue staining) of the 16 kDa protein band (on the polyacrylamide gel). The new PMC design is here!
Hsieh SY, Zhuang FH, Wu YT, Chen JK, Lee YL. It is believed that the high prevalence of disordered proteins in eukaryotes is related to intense signaling and regulatory activities take place in these organisms.24 Analyses of proteomes generally involve TCA-precipitation prior to detection of proteins on 2D gels. All experiments were performed at 25C. Many cross-peaks show significant chemical shift perturbation and some disappeared in the 1H-15N HSQC spectrum of the aFGF acquired in 5% w/v STCA [Fig. [Fig.1(B)].1(B)]. Biological processes and functions of proteins with long disordered regions. Genomic knowledge has vastly increased with advent of sophistication in methods used in proteomic analysis.13 Two-dimensional gel electrophoresis is the most powerful technique that is routinely used for protein separation and downstream proteomic analysis.4 One of the critical factors governing the success of proteomic analysis is the quality of the sample, which in turn is dependent on the protein extraction protocol(s) used.5,6 An ideal protein extraction procedure should reproducibly trap the most comprehensive repertoire of proteins possible with no or very minimal degradation and contamination by nonproteinaceous compounds.7,8 This is a daunting task because proteins not only have wide array of physicochemical properties like size, charge, hydrophobicity, but also show significant difference in their subcellular localization.9,10 In this background, it is a challenging task to design a generic extraction method to analyze the entire proteome. The lower stability of the STCA-induced MG-like intermediate is consistent with the loss of native tertiary structural interactions in the partially structured state. The intensity of the bands corresponding to the untreated aFGF was considered as a control for 100% protection against trypsin action. 1-anilino-8-naphthalene-sulfonate (ANS) binding experiments at various percentage of STCA (w/v) were performed using a Hitachi F-2500 spectrofluorimeter at 25C. To examine this aspect, aFGF precipitated using 30% w/v TCA was redissolved in 10 mM tris buffer (pH 7.5) containing different concentrations of sodium bicarbonate. [Fig.6(B-c)].6(B-c)]. The expression host strain E. coli BL21(DE3)pLysS is a vitamin B1-deficient host and hence the medium was supplemented with thiamine (vitamin B1). The proteins, aFGF, and lysozyme were treated with TCA and other acids using the method of Sagar et al.38 Protein solutions containing appropriate concentrations of the respective acids were prepared by the addition of requisite amounts of the stock solutions of the individual acids to aqueous solutions of proteins. The inset shows the emission spectra of the aFGF in native (continuous line) and denatured (dotted line) in 6M urea. All gel filtration experiments were carried out at various pH (at 25C) on a superdex-75 column using an AKTA FPLC device (Amersham Pharmacia Biotech). These results clearly demonstrate that unfolding of aFGF in STCA proceeds with the accumulation of an intermediate state(s) resembling the molten globule (MG). Size-exclusion chromatography (SEC) is a valuable technique to obtain information on the conformational changes that occur during the unfolding of proteins.32 SEC is an inert technique and is not known to perturb the equilibrium between the native, intermediate, and denatured states of proteins.32 In this context, the relative population of the various conformational states of aFGF, that may exist under various STCA concentrations, were monitored by SEC. To realize maximal expression yields, the composition of the M9 medium was modified by the addition of a mixture of vitamins. Sivaraman T, Kumar TKS, Jayaraman G, Yu C. The mechanism of 2,2,2-trichloroacetic acid-induced protein precipitation. S1-panel D). Trichloroacetic acid-induced molten globule state of aminoacylase from pig kidney. Results and reliability of protein quantification for two-dimensional gel electrophoresis strongly depend on the type of protein sample and the method employed.