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PubMed1994

Intracellular manipulation of disulfide bond formation in rotavirus proteins during assembly.

Rotavirus undergoes a unique mode of assembly in the rough endoplasmic reticulum (RER) of infected cells. Luminal RER proteins undergo significant cotranslational and posttranslational modifications, including disulfide bond formation. Addition of a reducing agent (dithiothreitol [DTT]) to rotavirus-infected cells did not significantly inhibit translation or disrupt established disulfide bonds in rotavirus proteins but prevented the formation of new disulfide bonds and infectious viral progeny. In DTT-treated, rotavirus-infected cells, all vp4, vp6, and ns28 epitopes but no vp7 epitopes were detected by immunohistochemical staining with a panel of monoclonal antibodies. When oxidizing conditions were reestablished in DTT-treated cells, intramolecular disulfide bonds in vp7 were rapidly and correctly established with the restoration of antigenicity, although prolonged DTT treatment led to the accumulation of permanently misfolded vp7. Electron microscopy revealed that cytosolic assembly of single-shelled particles and budding into the ER was not affected by DTT treatment but that outer capsid assembly was blocked, leading to the accumulation of single-shelled and enveloped intermediate subviral particles in the RER lumen.

Antigens, Viral↗
PubMed1996

Disulfide bonds of herpes simplex virus type 2 glycoprotein gB.

Glycoprotein B (gB) is the most highly conserved envelope glycoprotein of herpesviruses. The gB protein is required for virus infectivity and cell penetration. Recombinant forms of gB being used for the development of subunit vaccines are able to induce virus-neutralizing antibodies and protective efficacy in animal models. To gain structural information about the protein, we have determined the location of the disulfide bonds of a 696-amino-acid residue truncated, recombinant form of herpes simplex virus type 2 glycoprotein gB (HSV gB2t) produced by expression in Chinese hamster ovary cells. The purified protein, which contains virtually the entire extracellular domain of herpes simplex virus type 2 gB, was digested with trypsin under nonreducing conditions, and peptides were isolated by reversed-phase high-performance liquid chromatography (HPLC). The peptides were characterized by using mass spectrometry and amino acid sequence analysis. The conditions of cleavage (4 M urea, pH 7) induced partial carbamylation of the N termini of the peptides, and each disulfide peptide was found with two or three different HPLC retention times (peptides with and without carbamylation of either one or both N termini). The 10 cysteines of the molecule were found to be involved in disulfide bridges. These bonds were located between Cys-89 (C1) and Cys-548 (C8), Cys-106 (C2) and Cys-504 (C7), Cys-180 (C3) and Cys-244 (C4), Cys-337 (C5) and Cys-385 (C6), and Cys-571 (C9) and Cys-608 (C10). These disulfide bonds are anticipated to be similar in the corresponding gBs from other herpesviruses because the 10 cysteines listed above are always conserved in the corresponding protein sequences.

Amino Acid Sequence↗
PubMed2000

Variable-loop-deleted variants of the human immunodeficiency virus type 1 envelope glycoprotein can be stabilized by an intermolecular disulfide bond between the gp120 and gp41 subunits.

We have described an oligomeric gp140 envelope glycoprotein from human immunodeficiency virus type 1 that is stabilized by an intermolecular disulfide bond between gp120 and the gp41 ectodomain, termed SOS gp140 (J. M. Binley, R. W. Sanders, B. Clas, N. Schuelke, A. Master, Y. Guo, F. Kajumo, D. J. Anselma, P. J. Maddon, W. C. Olson, and J. P. Moore, J. Virol. 74:627-643, 2000). In this protein, the protease cleavage site between gp120 and gp41 is fully utilized. Here we report the characterization of gp140 variants that have deletions in the first, second, and/or third variable loop (V1, V2, and V3 loops). The SOS disulfide bond formed efficiently in gp140s containing a single loop deletion or a combination deletion of the V1 and V2 loops. However, deletion of all three variable loops prevented formation of the SOS disulfide bond. Some variable-loop-deleted gp140s were not fully processed to their gp120 and gp41 constituents even when the furin protease was cotransfected. The exposure of the gp120-gp41 cleavage site is probably affected in these proteins, even though the disabling change is in a region of gp120 distal from the cleavage site. Antigenic characterization of the variable-loop-deleted SOS gp140 proteins revealed that deletion of the variable loops uncovers cryptic, conserved neutralization epitopes near the coreceptor-binding site on gp120. These modified, disulfide-stabilized glycoproteins might be useful as immunogens.

Amino Acid Sequence↗
PubMed2000

ATP is required for correct folding and disulfide bond formation of rotavirus VP7.

Rotavirus is one of very few viruses that utilize the endoplasmic reticulum (ER) for assembly, and therefore it has been used as an attractive model to study ER-associated protein folding. In this study, we have examined the requirements for metabolic energy (ATP) for correct folding of the luminal and ER-associated VP7 of rotavirus. We found that VP7 rapidly misfolds in an energy-depleted milieu and is not degraded within 60 min. We also found that VP7 attained a stable minimum-energy state soon after translation in the ER. Most surprisingly, energy-misfolded VP7 could be recovered and establish correct disulfide bonds and antigenicity following a shift to an ATP-rich milieu. Using a Semliki Forest virus expression system, we observed that VP7 requires ATP and cellular, but not viral, factors for correct disulfide bond formation. Our results show for the first time that the disulfide bond formation of rotavirus VP7 is an ATP-dependent process. It has previously been shown that chaperones hydrolyze ATP during interaction with newly synthesized polypeptides and prevent nonproductive intra- and intermolecular interactions. The most reasonable explanation for the energy requirement of VP7 is thus a close interaction during folding with an ATP-dependent chaperone, such as BiP (Grp78), and possibly with protein disulfide isomerase. Taken together, our observations provide new information about folding of ER-associated proteins in general and rotavirus VP7 in particular.

Adenosine Triphosphate↗
PubMed2000

Disulfide bonds and membrane topology of the vaccinia virus A17L envelope protein.

The envelope protein encoded by the vaccinia virus A17L open reading frame is essential for virion assembly. Our mutagenesis studies indicated that cysteines 101 and 121 form an intramolecular disulfide bond and that cysteine 178 forms an intermolecular disulfide linking two A17L molecules. This arrangement of disulfide bonds has important implications for the topology of the A17L protein and supports a two-transmembrane model in which cysteines 101 and 121 are intraluminal and cysteine 178 is cytoplasmic. The structure of the A17L protein, however, was not dependent on these disulfide bonds, as a recombinant vaccinia virus with all three cysteine codons mutated to serines retained infectivity.

Blotting, Western↗
PubMed2000

The SU and TM envelope protein subunits of bovine leukemia virus are linked by disulfide bonds, both in cells and in virions.

After the polyprotein precursor of retroviral envelope proteins is proteolytically cleaved, the surface (SU) and transmembrane (TM) subunits remain associated with each other by noncovalent interactions or by disulfide bonds. Disulfide linkages confer a relatively stable association between the SU and TM envelope protein subunits of Rous sarcoma virus and murine leukemia virus. In contrast, the noncovalent association between SU and TM of human immunodeficiency virus leads to significant shedding of SU from the surface of infected cells. The SU and TM proteins of bovine leukemia virus (BLV) initially were reported to be disulfide linked but later were concluded not to be, since TM is often lost during purification of SU protein. Here, we show that SU and TM of BLV do, indeed, associate through disulfide bonds, whether the envelope proteins are overexpressed in transfected cells, are produced in virus-infected cells, or are present in newly produced virions.

Animals↗
PubMed2001

Roles of disulfide linkage and calcium ion-mediated interactions in assembly and disassembly of virus-like particles composed of simian virus 40 VP1 capsid protein.

The simian virus 40 capsid is composed of 72 pentamers of VP1 protein. Although the capsid is known to dissociate to pentamers in vitro following simultaneous treatment with reducing and chelating agents, the functional roles of disulfide linkage and calcium ion-mediated interactions are not clear. To elucidate the roles of these interactions, we introduced amino acid substitutions in VP1 at cysteine residues and at residues involved in calcium binding. We expressed the mutant proteins in a baculovirus system and analyzed both their assembly into virus-like particles (VLPs) in insect cells and the disassembly of those VLPs in vitro. We found that disulfide linkages at both Cys-9 and Cys-104 conferred resistance to proteinase K digestion on VLPs, although neither linkage was essential for the formation of VLPs in insect cells. In particular, reduction of the disulfide linkage at Cys-9 was found to be critical for VLP dissociation to VP1 pentamers in the absence of calcium ions, indicating that disulfide linkage at Cys-9 prevents VLP dissociation, probably by increasing the stability of calcium ion binding. We found that amino acid substitutions at carboxy-terminal calcium ion binding sites (Glu-329, Glu-330, and Asp-345) resulted in the frequent formation of unusual tubular particles as well as VLPs in insect cells, indicating that these residues affect the accuracy of capsid assembly. In addition, unexpectedly, amino acid substitutions at any of the calcium ion binding sites tested, especially at Glu-157, resulted in increased stability of VLPs in the absence of calcium ions in vitro. These results suggest that appropriate affinities of calcium ion binding are responsible for both assembly and disassembly of the capsid.

Animals↗
PubMed1996

Human interleukin-3 (IL-3) induces disulfide-linked IL-3 receptor alpha- and beta-chain heterodimerization, which is required for receptor activation but not high-affinity binding.

The human interleukin-3 receptor (IL-3R) is a heterodimer that comprises an IL-3 specific alpha chain (IL-3R alpha) and a common beta chain (beta C) that is shared with the receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-5. These receptors belong to the cytokine receptor superfamily, but they are structurally and functionally more related to each other and thus make up a distinct subfamily. Although activation of the normal receptor occurs only in the presence of ligand, the underlying mechanisms are not known. We show here that human IL-3 induces heterodimerization of IL-3R alpha and beta c and that disulfide linkage of these chains is involved in receptor activation but not high-affinity binding. Monoclonal antibodies (MAb) to IL-3R alpha and beta c were developed which immunoprecipitated, in the absence of IL-3, the respective chains from cells labelled with 125I on the cell surface. However, in the presence of IL-3, each MAb immunoprecipitated both IL-3R alpha and beta c. IL-3-induced receptor dimers were disulfide and nondisulfide linked and were dependent on IL-3 interacting with both IL-3R alpha and beta c. In the presence of IL-3 and under nonreducing conditions, MAb to either IL-3R alpha or beta c immunoprecipitated complexes with apparent molecular weights of 215,000 and 245,000 and IL-3R alpha and beta c monomers. Preincubation with iodoacetamide prevented the formation of the two high-molecular-weight complexes without affecting noncovalent dimer formation or high-affinity IL-3 binding. Two-dimensional gel electrophoresis and Western blotting (immunoblotting) demonstrated the presence of both IL-3R alpha and beta c in the disulfide-linked complexes. IL-3 could also be coimmunoprecipitated with anti-IL-3R alpha or anti-beta c MAB, but it was not covalently attached to the receptor. Following IL-3 stimulation, only the disulfide-linked heterodimers exhibited reactivity with antiphosphotyrosine antibodies, with beta c but not IL-3R alpha being the phosphorylated species. A model of IL-3R activation is proposed which may be also applicable to the related GM-CSF and IL-5 receptors.

Animals↗
PubMed1987

Disulfide-linked membrane proteins in X-ray-induced cataract.

The formation of membrane protein disulfide was investigated at various stages of development of X-ray-induced cataract in the rabbit. Intermolecular disulfide bonding of lens membrane proteins was detected not only in the mature cataract (occurring 8-9 weeks after the X-ray dose) but also at 1 week prior to maturation, in which no significant increase in lens hydration occurs and where opacification is confined mainly to the posterior subcapsular region. Two-dimensional diagonal electrophoresis revealed that polypeptides with apparent molecular weights of 21, 23, 25, 31, 35, 46 and 53 kilodaltons were involved in cross-linking. The MP26 membrane polypeptide was not significantly involved in the disulfide bonding. The oxidation of membrane proteins in stages other than mature was evident only in the lens nucleus (which remained clear) and not in the cortex. The results of this study indicate that an intermolecular disulfide linkage of cytosolic proteins to membranes occurs prior to formation of mature cataract, and may be a precursor to protein aggregation and insolubilization in the mature nuclear cataract.

Animals↗
PubMed1975

Ozone interaction with rodent lung. III. Oxidation of reduced glutathione and formation of mixed disulfides between protein and nonprotein sulfhydryls.

Nonprotein sulfhydryls (NPSH), a major source of cellular reducing substances, were examined in lung tissue after short-term exposure of rats to O3. While the NPSH level was unaffected by low-level exposures (e.g., 0.8 ppm for up to 24 h or 1.5 ppm for up to 8 h), it was significantly lowered by higher exposure regimens (e.g., 25 per cent after 2 ppm for 8 h and 49 per cent after 4 ppm for 6 h). After exposure to 4 ppm O3 for 6 h the level of reduced glutathione (GSH), which accounted for approximately 90 per cent of NPSH in the lung, decreased 40 per cent but without a rise in the level of oxidized gluathione (GSSG). Treatment of lung homogenate with borohydride led to recovery of NPSH in exposed lungs to control values, suggesting that NPSH or GSH oxidation during in vivo O3 exposure resulted in formation of mixed disulfides with other sulfhydryl (SH) groups of lung tissue. Extracts of borohydride-treated particulate and supernatant fractions of lung homogenate were analyzed for NPSH by paper chromatography. From this analysis GSH appeared to be the only NPSH bound to lung tissue proteins via mixed disulfide linkage. The formation of mixed disulfides appeared to be a transient phenomenon. Immediately after a 4-h exposure to 3 ppm O3 the level of mixed disulfides was small (15 per cent of the total NPSH) but attained a peak (equivalent to 0.6 mumol NPSH/lung) after a recovery for 24 h. However, the level diminished considerably within 48 h of recovery.

Animals↗
PubMed2005

A two disulfide bridge Kazal domain from Phytophthora exhibits stable inhibitory activity against serine proteases of the subtilisin family.

BACKGROUND: Kazal-like serine protease inhibitors are defined by a conserved sequence motif. A typical Kazal domain contains six cysteine residues leading to three disulfide bonds with a 1-5/2-4/3-6 pattern. Most Kazal domains described so far belong to this class. However, a novel class of Kazal domains with two disulfide bridges resulting from the absence of the third and sixth cysteines have been found in biologically important molecules, such as human LEKTI, a 15-domain inhibitor associated with the severe congenital disease Netherton syndrome. These domains are referred to as atypical Kazal domains. Previously, EPI1, a Kazal-like protease inhibitor from the oomycete plant pathogen Phytophthora infestans, was shown to be a tight-binding inhibitor of subtilisin A. EPI1 also inhibits and interacts with the pathogenesis-related P69B subtilase of the host plant tomato, suggesting a role in virulence. EPI1 is composed of two Kazal domains, the four-cysteine atypical domain EPI1a and the typical domain EPI1b. RESULTS: In this study, we predicted the inhibition constants of EPI1a and EPI1b to subtilisin A using the additivity-based sequence to reactivity algorithm (Laskowski algorithm). The atypical domain EPI1a, but not the typical domain EPI1b, was predicted to have strong inhibitory activity against subtilisin A. Inhibition assays and coimmunoprecipitation experiments showed that recombinant domain EPI1a exhibited stable inhibitory activity against subilisin A and was solely responsible for inhibition and interaction with tomato P69B subtilase. CONCLUSION: The finding that the two disulfide bridge atypical Kazal domain EPI1a is a stable inhibitor indicates that the missing two cysteines and their corresponding disulfide bond are not essential for inhibitor reactivity and stability. This report also suggests that the Laskowski algorithm originally developed and validated with typical Kazal domains might operate accurately for atypical Kazal domains.

Amino Acid Sequence↗
PubMed1994

Treatment of IM-9 cells with human growth hormone (GH) promotes rapid disulfide linkage of the GH receptor.

Human GH (hGH) is believed to elicit its signal by promoting dimerization of the hGH receptor (hGHR). In this study, we examined a covalent linkage of receptors induced by hGH treatment of IM-9 cells. hGH induced a time- and concentration-dependent appearance of a disulfide-linked species of 215-230 kilodaltons, designated p215-230, that at 37 C was long-lived (> 1 h). p215-230 was confirmed to contain the hGHR (115-140 kilodaltons) as at least one of its constituents by two-dimensional diagonal sodium dodecyl sulfate-polyacrylamide gel electrophoresis. hGH induction of p215-230 required intact cells and was inhibitable by pretreatment of cells with N-ethylmaleimide (NEM), a sulfhydryl-reactive alkylating agent. NEM pretreatment did not, however, prevent hGH-dependent formation of a nondisulfide-linked p215-230 form, which was detected in NEM-pretreated hGH-stimulated cells by chemical cross-linking of detergent cell extracts. The disulfide-linked form of the hGHR accounted for a substantial fraction of the receptors that became tyrosine phosphorylated early into hGH treatment. However, formation of the disulfide-linked hGHR was not blocked by attenuation of tyrosine kinase activation, in that pretreatment of cells with staurosporine (1.25 microM) prevented detectable hGH-induced tyrosine phosphorylation without preventing the appearance of p215-230. These findings indicate that hGH induces its receptor to form a noncovalently associated complex, which then undergoes a rapid transition to a disulfide-linked form. These processes may have relevance to hGH signaling and/or hGHR trafficking.

B-Lymphocytes↗
PubMed1996

Disulfide bonds 7-31 and 59-87 of the alpha-subunit play a different role in assembly of human chorionic gonadotropin and lutropin.

CG, LH, FSH, and TSH are a family of heterodimeric glycoprotein hormones that contain a common alpha-subunit but differ in their hormone-specific beta-subunits. Both subunits have five and six disulfide bonds, respectively, which consists of cystine knot structure. We previously eliminated the disulfide bonds 7-31 and 59-87 in alpha-subunit without significantly affecting assembly with human CG beta-subunit. To study the role of these disulfide bonds in dimerization with other beta-subunits, the wild-type or mutated alpha gene was contransfected with the wild-type human LH beta or FSH beta gene into Chinese hamster ovary (CHO) cells or GH3 cells, and assembly was assessed by continuous labeling with [35S]methionine/cysteine, immunoprecipitation with anti-alpha or-beta serum, and SDS-PAGE. Our data revealed that disruption of either disulfide bond 7-31 or 59-87 in the alpha-subunit markedly reduced the dimer formation with LH beta-subunit in both CHO and GH3 cells, whereas it did not significantly affect the assembly of FSH. This suggests that the regions in the alpha-subunit recognized by beta-subunits for assembly are different among gonadotropins.

Animals↗
PubMed1997

Characterization of soluble, disulfide bond-stabilized, prokaryotically expressed human thyrotropin receptor ectodomain.

To study the interaction of TSH receptor (TSHR) autoantibodies with receptor protein; it is necessary first to express the receptor in the proper conformation including the formation of correct disulfide bridges. However, the reducing environment of the Escherichia coli (E. coli) cytoplasm prevents the generation of protein disulfide bonds and limits the solubility and immunoreactivity of recombinant human TSHR (hTSHR) products. To circumvent these limitations, hTSHR complementary DNA encoding the extracellular domain (hTSHR-ecd; amino acids 21-415) was inserted into the vector pGEX-2TK by directional cloning and used to transform the thioredoxin reductase mutant strain of E. coli (Ad494), which allowed formation of disulfide bonds in the cytoplasm. After induction, the expressed soluble hTSHR-ecd fusion protein was detected by Western blot analysis using a monoclonal antibody directed against hTSHR amino acids 21-35. This showed that over 50% of the expressed hTSHR-ecd was soluble in contrast to expression in a wild-type E. coli (strain alpha F'), where the majority of the recombinant receptor was insoluble. The soluble recombinant receptor was affinity purified and characterized. Under nonreducing SDS-PAGE conditions, the soluble hTSHR-ecd migrated as refolded, disulfide bond-stabilized, multimeric species, whose formation was independent of fusion partner protein. This product was found to be biologically active as evidenced by the inhibition of the binding of 125I-TSH to the full-length hTSHR expressed in transfected CHO cells and was used to develop a competitive capture enzyme-linked immunosorbent assay for mapping of hTSHR antibody epitopes. Hence, hTSHR-ecd produced in bacteria with a thioredoxin reductase mutation was found to be highly soluble and biologically relevant.

Antibodies↗
PubMed2005

Growth suppressing effect of garlic compound diallyl disulfide on prostate cancer cell line (PC-3) in vitro.

Prostate cancer is the most predominant cancer in men and prostate cancer related death increases every year. Till date, there is no effective therapy other than androgen ablation therapy. At this stage, induction of apoptosis is considered as a better strategy to control cancer. Previous studies reported that aged garlic extract suppresses cancer growth and enhances immune system against cancer. In the present study, diallyl disulfide, oil soluble organosulfur compound of garlic, was studied for its antiproliferative effect on prostate cancer cells in vitro. The suppression of cell growth was demonstrated by [(3)H]thymidine incorporation assay. Induction of DNA damage was assessed by agarose gel electrophoresis. The results showed that diallyl disulfide inhibited the growth of prostate cancer cells in a dose dependent manner, compared to the control. At 50 microM and 100 microM concentrations, diallyl disulfide induced DNA damage in PC-3 cells. It is concluded that diallyl disulfide, component of aged garlic extract, inhibits proliferation of prostate cancer cells through the induction of apoptosis.

Allyl Compounds↗
PubMed1996

Amino acids and peptides. XXVII. Solid phase synthesis of fibrinogen-related peptides with disulfide bond formed on solid support.

Fibrinogen-related peptides, monomeric cyclic peptides through a disulfide bond [cyclo(H-Cys-Arg-Gly-Asp-Phe-Cys-NH2), cyclo(H-Cys-Arg-Gly-Asp-Phe-Cys-Gly-NH2), cyclo(H-Cys-Arg-Gly-Asp-Cys-NH2) and cyclo(H-Cys-Arg-Gly-Asp-Cys-Gly-NH2)], were prepared by the solid phase method with disulfide bond formation on the solid support. The acetamidomethyl group was used for protection of the thiol group of Cys and synthetic peptide-resins were treated with iodine to give the disulfide bond. Monomeric cyclic peptides were obtained as main products. Purified S-acetamidomethylated peptides were also oxidized with iodine, but the desired materials could not be isolated by HPLC. The disulfide formation from S-acetamidomethylcysteine-containing peptide resin by iodine treatment on the solid support was more effective than that from S-acetamidomethylcysteine-containing peptide. The inhibitory effect of the cyclic peptides on platelet aggregation were much more potent than that of H-Arg-Gly-Asp-NH2.

Amino Acid Sequence↗
PubMed2000

[A novel synthetic approach of tryptophan-containing cystine peptides by regioselective disulfide bond-forming reaction using the silyl chloride-sulfoxide system].

A general scheme for the efficient synthesis of Trp-containing cystine peptide by the successive treatment with methyltrichlorosilane-diphenylsulfoxide in trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TFMSA)-thioanisole in TFA, is described. A disulfide bond-forming reaction by silyl chloride-sulfoxide system is completed within 10-15 min without modifications at sensitive residues (Tyr, His, Met) in peptide chain, except for a Trp residue. In order to synthesize a Trp-containing cystine peptide using silyl chloride, the indole moiety of Trp has to be protected since the chlorination of the indole ring proceeded predominantly. A formyl group has been the only protecting group employed for this purpose in practical syntheses of cystine peptides, although it was clarified that a side reaction derived from the formyl group migration was inevitable in the synthesis of somatostatin. Firstly, we examined the application of the following Nin-protecting groups, mesitylene-2-sulfonyl (Mts), cyclohexyloxycarbonyl (Hoc), and 2,4-dimethylpent-3-yloxycarbonyl(Doc) for an efficient synthesis of the Trp-containing cystide peptide by the silyl chloride method. In order to find a feasible scheme of the successive treatment with CH3SiCl3-PhS(O)Ph/TFA and TFMSA-thianisole in TFA, we synthesized somatostatin using Trp(Mts), Trp(Hoc) or Trp(Doc) derivative. The Doc group was found to be the most suitable as an indole protecting group, since the protecting group was cleaved under mild conditions (4 degrees C, 30 min) via the corresponding Nin-carboxylic acid intermediate. We then applied the above procedure to the synthesis of endothelin-1 (ET-1), a peptide containing 21-amino acid residues having a C-terminal Trp residue and two disulfide bonds, by regioselective disulfide formation. The combination of the silyl chloride method with iodine oxidation using S-acetamidomethyl (Acm) and S-tBu groups for the regioselective double disulfide formation was successfully applied to give a highly purified ET-1. These results also show that the Nin-Doc group would be useful for the efficient syntheses of complex cystine-peptides by the silyl chloride method.

Amino Acid Sequence↗
PubMed1993

Limited proteolysis of disulfide-reduced ovalbumin by subtilisin.

Our previous study [Takahashi et al., J. Biochem., 109, 846-851 (1991)] has shown that the disulfide-reduced form of ovalbumin was proteolyzed by subtilisin into three major fragments. It was investigated whether or not these three fragments would be folded into one molecule. Gel permeation and ion-exchange chromatography indicated that the three fragments were eluted in a single peak. The proteolyzed protein had a CD spectrum that was almost indistinguishable from the disulfide-reduced, non-proteolyzed form of ovalbumin. Differential scanning calorimetry, however, revealed that the proteolyzed ovalbumin was denatured at a lower temperature than that of the disulfide-reduced, non-proteolyzed protein. Thus, it is concluded that the three fragments were folded into a native-like conformation with decreased stability. Chemical analyses of the fragments purified by reverse-phase HPLC revealed that there was a cleavage site in the disulfide-reduced form of ovalbumin, at least at the amino-terminal side of Cys(73), in addition to the well-known cleavage sites in plakalbumin.

Amino Acid Sequence↗