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Naja atra cardiotoxins enhance the protease activity of chymotrypsin. Int J Biol Macromol 2019; 136:512-520. [PMID: 31199971 DOI: 10.1016/j.ijbiomac.2019.06.066] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Revised: 05/27/2019] [Accepted: 06/11/2019] [Indexed: 02/03/2023]
Abstract
Snake venom cardiotoxins (CTXs) present diverse pharmacological functions. Previous studies have reported that CTXs affect the activity of some serine proteases, namely, chymotrypsin, subtilisin, trypsin, and acetylcholinesterase. To elucidate the mode of action of CTXs, the interaction of CTXs with chymotrypsin was thus investigated. It was found that Naja atra CTX isotoxins concentration-dependently enhanced chymotrypsin activity. The capability of CTX1 and CTX5 in increasing chymotrypsin activity was higher than that of CTX2, CTX3, and CTX4. Removal of the molecular beacon-bound CTXs by chymotrypsin, circular dichroism measurement, and acrylamide quenching of Trp fluorescence indicated that CTXs bound to chymotrypsin. Chemical modification of Lys, Arg, or Met residues of CTX1 attenuated its capability to enhance chymotrypsin activity without impairing their bond with chymotrypsin. Catalytically inactive chymotrypsin retained the binding affinity for native and modified CTX1. CTX1 and chemically modified CTX1 differently altered the global conformation of chymotrypsin and inactivated chymotrypsin. Moreover, CTX1 did not reduce the interaction of 2-(p-toluidino)-naphthalene-6-sulfonate (TNS) with chymotrypsin and inactivated chymotrypsin. Together with previous results revealing that TNS can bind at the hydrophobic region of active site in chymotrypsin, our data suggest that CTXs can enhance chymotrypsin activity by binding to the region outside the enzyme's active site.
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Li X, Zhou S, Wang Y, Lian H, Zuo A, Zhou K, Tong L, Zhou Z, Gao J. The pilot-scale preparation of the SA-hGM-CSF bi-functional fusion protein. Bioengineered 2019; 10:108-120. [PMID: 31017543 PMCID: PMC6527079 DOI: 10.1080/21655979.2019.1608712] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The granulocyte-macrophage colony-stimulating factor (GM-CSF) can be used to induce a powerful immune response. Based on the specific binding of biotin and streptavidin, SA-hGM-CSF was anchored on the surface of biotinylated tumor cells, which could enhance the anti-tumor effect of tumor cell vaccines in our previous reports, suggesting it would have potential clinical value. Preparation of the biologically active proteins in large-scale production is the basis of clinical application, however, only a small amount of biologically active protein was obtained according to previous studies. In this study, we researched the effects of various factors on the purification and simultaneous renaturation of SA-hGM-CSF fusion protein by single factor experiment and orthogonal experiment. Here, we developed a viable pilot-scale trial in the fermentation, purification, refolding and freeze-drying of SA-hGM-CSF proteins in order to efficiently obtain more biologically active proteins with high purity, which will lay the foundation for industrial production.
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Affiliation(s)
- Xiaoqing Li
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Shirong Zhou
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Yao Wang
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Hui Lian
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Anxin Zuo
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Kaihua Zhou
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Ling Tong
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Zhujun Zhou
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
| | - Jimin Gao
- a Zhejiang Provincial Key Lab for Technology & Application of Model Organisms,School of Laboratory Medicine and Life Sciences , Wenzhou Medical University , Wenzhou , China
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Chang LS, Lin SR, Huang HB. Disulfide isomerization and thiol-disulfide exchange of long neurotoxins from the venom of Ophiophagus hannah. Arch Biochem Biophys 2006; 454:181-8. [PMID: 16962984 DOI: 10.1016/j.abb.2006.08.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Revised: 08/02/2006] [Accepted: 08/03/2006] [Indexed: 10/24/2022]
Abstract
Selective reduction on the Cys28-Cys32 disulfide of Ophiophagus hannah neurotoxins, Oh-4 and Oh-5, revealed that isomerization of this disulfide linkage caused the two toxins to have distinct conformation and different retention time on a reversed-phase column. The Cys28-Cys32 disulfide of Oh-4 and Oh-5 was prone to form mixed disulfides with glutathione following pseudo-first-order kinetics. In addition to glutathionylated proteins, Oh-4 could be promoted to convert into Oh-5 by thiol compounds. Isomerization of Oh-5 into Oh-4 was not observed in the presence of thiol compounds. Dethiolation of glutathionylated proteins produced Oh-4 and Oh-5. Oxidation of the partially reduced toxin with reduced Cys28 and Cys32 was exclusively converted into Oh-5 regardless of the absence or presence of GSH/GSSG. Acrylamide quenching studies revealed difference in degree of exposure of the single Trp27 between Oh-4 and Oh-5. Synthesized peptides with substitution of Trp27 or Phe31 with Gly abolished entirely the formation of disulfide-linked dimeric product noted with the peptide of wild-type sequence. These results suggest that disulfide formation and isomerization of Cys28-Cys32 could be regulated by thiolation, and that the bulky aromatic residues Trp27 and Phe31 facilitate favorably the occurrence of disulfide isomerization of Cys28-Cys32.
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Affiliation(s)
- Long-Sen Chang
- Institute of Biomedical Sciences, National Sun Yat-Sen University-Kaohsiung Medical University Joint Center, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.
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Pergolizzi RG, Ropper AE, Dragos R, Reid AC, Nakayama K, Tan Y, Ehteshami JR, Coleman SH, Silver RB, Hackett NR, Menez A, Crystal RG. In vivo trans-splicing of 5' and 3' segments of pre-mRNA directed by corresponding DNA sequences delivered by gene transfer. Mol Ther 2004; 8:999-1008. [PMID: 14664803 DOI: 10.1016/j.ymthe.2003.08.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
We have developed a new paradigm of in vivo gene transfer termed "segmental trans-splicing" (STS), in which individual "donor" and "acceptor" DNA sequences, delivered in vitro or in vivo, generate pre-mRNAs with 5' and 3' splice signals, respectively, and complementary hybridization domains through which the two pre-mRNAs interact, facilitating trans-splicing of the two mRNA fragments. To demonstrate STS, we used alpha-cobratoxin, a neurotoxin that binds irreversibly to postsynaptic nicotinic acetylcholine receptors. Cells or animals receiving both donor and acceptor plasmids, but neither plasmid alone, yielded RT-PCR products with the correct sequence of mature alpha-cobratoxin mRNA, suggesting that trans-splicing had occurred. Mice receiving intravenous administration of > or = 7.5 microg donor + acceptor plasmids, but not either plasmid alone, died within 6 h. These data demonstrate that segmental trans-splicing occurs in vivo. This approach should permit the intracellular assembly of molecules hitherto too large to be accommodated within current gene transfer vectors.
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Affiliation(s)
- Robert G Pergolizzi
- Belfer Gene Therapy Core Facility, Weill Medical College of Cornell University, New York, New York 10021, USA
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Klimes I, Weston K, Kovacs P, Gasperikova D, Jezova D, Kvetnansky R, Thompson JR, Sebokova E, Samani NJ. Mapping of genetic loci predisposing to hypertriglyceridaemia in the hereditary hypertriglyceridaemic rat: analysis of genetic association with related traits of the insulin resistance syndrome. Diabetologia 2003; 46:352-8. [PMID: 12687333 DOI: 10.1007/s00125-003-1035-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/16/2002] [Revised: 10/11/2002] [Indexed: 10/20/2022]
Abstract
AIMS/HYPOTHESIS Hypertriglyceridaemia is an important risk factor for coronary heart disease, especially in the context of the insulin resistance syndrome where it often occurs with hypertension. The two phenotypes are also associated in the hereditary hypertriglyceridaemic (hHTg) rat. The aim of this study was to map quantitative trait loci that affect plasma triglyceride concentration in the hHTg rat and determine whether they co-localize with loci for blood pressure. METHODS Second filial generation progeny (n=189) from a cross of the hHTg rat with the Brown Norway rat were phenotyped for fasting plasma triglyceride, glucose and insulin concentrations, and direct unrestrained resting blood pressure. A partial genome-scan was conducted using 153 microsatellite markers that were polymorphic between the two strains. RESULTS A major locus (lod score 6.5) influencing plasma triglyceride concentration in a co-dominant fashion was mapped to chromosome 4 between D1Mit 5 and D1Mit17. Chromosome 8 contained multiple peaks with a lod score greater than 4.0 influencing triglyceride concentration. Importantly, none of the triglyceride loci had an effect on blood pressure. The triglyceride locus on chromosome 4 co-localized with a locus for fasting plasma insulin (lod score 4.1), although the effect on insulin concentration was in the opposite direction to that on triglyceride. CONCLUSION/INTERPRETATION We have mapped the major loci that affect plasma triglyceride concentration in the hHTg rat. These loci do not influence blood pressure suggesting that these commonly associated phenotypes of the insulin resistance syndrome are not be due to pleiotropic effects of the same gene(s).
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Affiliation(s)
- I Klimes
- Diabetes and Nutrition Research Laboratory, Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovakia
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Meng QX, Wang WY, Lu QM, Jin Y, Wei JF, Zhu SW, Xiong YL. A novel short neurotoxin, cobrotoxin c, from monocellate cobra (Naja kaouthia) venom: isolation and purification, primary and secondary structure determination, and tertiary structure modeling. Comp Biochem Physiol C Toxicol Pharmacol 2002; 132:113-21. [PMID: 12039691 DOI: 10.1016/s1532-0456(02)00049-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A novel short neurotoxin, cobrotoxin c (CBT C) was isolated from the venom of monocellate cobra (Naja kaouthia) using a combination of ion-exchange chromatography and FPLC. Its primary structure was determined by Edman degradation. CBT C is composed of 61 amino acid residues. It differs from cobrotoxin b (CBT B) by only two amino acid substitutions, Thr/Ala11 and Arg/Thr56, which are not located on the functionally important regions by sequence similarity. However, the LD50 is 0.08 mg/g to mice, i.e. approximately five-fold higher than for CBT B. Strikingly, a structure-function relationship analysis suggests the existence of a functionally important domain on the outside of Loop III of CBT C. The functionally important basic residues on the outside of Loop III might have a pairwise interaction with alpha subunit, instead of gamma or delta subunits of the nicotinic acetylcholine receptor (nAChR).
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Affiliation(s)
- Qing-Xiong Meng
- Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, PR China
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Chang LS, Lin SR, Yang CC. Glutaraldehyde cross-linking alters the environment around Trp(29) of cobrotoxin and the pathway for regaining its fine structure during refolding. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 2001; 58:173-9. [PMID: 11532076 DOI: 10.1034/j.1399-3011.2001.00909.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Cobrotoxin, purified from the venom of Naja naja atra (Taiwan cobra), was subjected to modification with glutaraldehyde in order to prepare intra- and intermolecule cross-linked derivatives. Monomeric and dimeric derivatives were separated from polymeric derivatives by gel filtration. The results of amino acid analysis and sequence determination revealed that only Lys residues were selectively modified by glutaraldehyde. Glutaraldehyde cross-linking was accompanied by a change in the gross conformation of cobrotoxin as revealed by circular dichroism spectra of the modified derivatives. Compared with cobrotoxin, Trp(29) of monomeric and dimeric derivatives was in an apolar microenvironment. This was in agreement with acrylamide quenching studies showing that the spatial position of the Trp indole ring became buried in the interior of the molecule after glutaraldehyde cross-linking. Moreover, the Trp of modified derivatives was less accessible for iodide than that observed with cobrotoxin. Notably, disulfide reduction could not completely unfold the structure of glutaraldehyde-modified derivatives as evidenced by the results of acrylamide quenching studies and enzyme-linked immunoassay. Study of the characteristic changes in Trp fluorescence after the initiation of refolding suggested that the fine structure around Trp(29) of cobrotoxin and glutaraldehyde-modified derivatives was formed differently. These results suggest that glutaraldehyde cross-linking leads to a change in the microenvironment of cobrotoxin Trp(29) and alters the pathway of its fine structure formation during the refolding of cobrotoxin.
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Affiliation(s)
- L S Chang
- Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan.
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Chang LS, Lin SR, Yang CC. Refolding of Taiwan cobra neurotoxin: intramolecular cross-link affects its refolding reaction. Arch Biochem Biophys 2001; 387:289-96. [PMID: 11370853 DOI: 10.1006/abbi.2000.2236] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In order to explore the effect of intramolecular cross-linking in the folding reaction of cobrotoxin from Naja naja atra (Taiwan cobra) venom, the toxin molecule was modified with glutaraldehyde (GA). The monomeric GA-modified cobrotoxin (mGA-cobrotoxin) was separated from the dimeric and trimeric derivatives using gel filtration. The results of electrophoretic and chromatographic analyses revealed that mGA-cobrotoxin comprised two modified derivatives, which contained modified Lys residues at positions 26 and 27 and at positions 26, 27, and 47, respectively. Moreover, an intramolecular cross-linking of loops II and III by Lys residues was noted with the monomeric derivative containing three modified Lys residues. In sharp contrast to cobrotoxin observations, the folding rate of mGA-cobrotoxin decreased in the presence of GSH/ GSSG, but notably increased in the absence of thiol compounds. Particularly, the accelerated effect of GSH/GSSG on the refolding reaction was affected by the presence of the intramolecular cross-link. Comparative analyses on cobrotoxin and mGA-cobrotoxin CD spectra revealed that modification with the GA reagent caused a change in the gross conformation of cobrotoxin. Fluorescence measurement revealed that the stability of the microenvironment around the single Trp-29 in mGA-cobrotoxin and unfolded mGA-cobrotoxin was appreciably higher than in cobrotoxin and unfolded toxin. Moreover, the ordered structure formation around Trp-29 in refolded mGA-cobrotoxin was faster than in refolded cobrotoxin as evidenced by fluorescence quenching studies. Taken together, these results suggest that the structural flexibility of unfolded cobrotoxin should be favorable for the thiol catalyst to exert its action in the refolding reaction after modification with GA.
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Affiliation(s)
- L S Chang
- Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan.
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Chang L, Chang C, Lin S. Differential contribution of the conserved tyrosine residues to activity and structural stability of Ophiophagus hannah alpha-neurotoxins. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 2000; 55:240-5. [PMID: 10727106 DOI: 10.1034/j.1399-3011.2000.00176.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Two alpha-neurotoxins, Oh-4 and Oh-7, from king cobra (Ophiophagus hannah) venom were subjected to Tyr modification with tetranitromethane. Selective nitration of Tyr4 in Oh-4 caused a slight decrease in lethal toxicity of 11% and a decrease in nicotinic acetylcholine receptor (nAchR)-binding activity of 28%, whereas nitration of Tyr4 in Oh-7 resulted in an approximately equal 60% decrease in lethality and nAchR-binding activity. When the Tyr23 in Oh-4 or Tyr22 in Oh-7 appears to be 'buried' in the toxin following further modification, the toxins lost their biological activity and conformational change concurrently. Nevertheless, the dinitrated Oh-4 retained a beta-sheet structure as revealed by CD spectra and exhibited a precipitin reaction with anti-Oh-4 sera. These results indicate that both Tyr4 and Tyr22 play a crucial role in the neurotoxicity of Oh-7, whereas intact Tyr23 is involved in the manifestation of the toxicity of Oh-4 to a greater extent. In contrast to Oh-4, the conformational stability of Oh-7 depends heavily upon the integrity of Tyr22.
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Affiliation(s)
- L Chang
- Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan.
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Chang LS, Chen KC, Wu BN, Lin SK, Wu PF, Hong YR, Yang CC. Expression and mutagenesis studies of cobrotoxin from Taiwan cobra. Biochem Biophys Res Commun 1999; 263:652-6. [PMID: 10512733 DOI: 10.1006/bbrc.1999.1418] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The cDNA encoding cobrotoxin was constructed from the cellular RNA isolated from the venom glands of Naja naja atra (Taiwan cobra). The cDNA was subcloned into the expression vector pET20b(+) and transformed into BL21(DE3) Escherichia coli strain. Expressed cobrotoxin was isolated from inclusion bodies of E. coli and subjected to refolding into its folded structure. The refolded cobrotoxin was purified by high-performance liquid chromatography and exhibited a neurotoxicity in inhibiting acetylcholine-induced muscle contractions. Recombinant cobrotoxin showed a tendency to isomerize its disulfide bonds as that observed with native cobrotoxin. An appreciable decrease in the rate of isomerization reaction was observed when Glu-38 was replaced with Gln-38 or Lys-47 was replaced with Glu-47 or Gln-47. These results reflect that the element in controlling the disulfide isomerization of cobrotoxin is closely associated with the charged side chains in the cobrotoxin molecule.
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Affiliation(s)
- L S Chang
- Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan, 804.
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Lin SR, Chang LS, Chang CC. Disulfide isomers of alpha-neurotoxins from King cobra (Ophiophagus hannah) venom. Biochem Biophys Res Commun 1999; 254:104-8. [PMID: 9920740 DOI: 10.1006/bbrc.1998.9888] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Two novel alpha-neurotoxins, Oh-6A and Oh-6B, isolated from the king cobra (Ophiophagus hannah) venom, consist of 70 amino acid residues with 10 cysteine residues and share the same amino acid sequences as determined by Edman degradation on the peptide fragments generated from the proteolytic hydrolysates. Their sequences share 46-53% homology with Oh-4, Oh-5, Toxin a, and Toxin b from the same venom. The finding that Oh-6A and Oh-6B had different retention times in the reversed-phase column suggested that the two toxin molecules should not have the same conformation. Selective reduction on the disulfide bond, Cys26--Cys30, at the tip of their loop II structures resulted in the production of the partially reduced derivatives eluted at the same position. Under redox conditions, the partially reduced Oh-6A and 6B exclusively converted into native Oh-6A as evidenced by HPLC analyses. This suggests that Oh-6A and Oh-6B are disulfide isomers which probably arise from cis-trans isomerization of the Cys26--Cys30 disulfide bond. Alternatively, the two toxins exhibited binding activity toward nAChR and lethal toxicity equally. It reflects that the diversity around the extra loop at the loop II structure does not exert a significant effect on the manifestation of the neurotoxicity of Oh-6A and Oh-6B.
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Affiliation(s)
- S R Lin
- School of Chemistry, Kaohsiung Medical College, Kaohsiung, Taiwan, 807, Republic of
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Chang L, Lin S, Chang C, Yang C. Disulfide isomerization within the C-terminus of cobrotoxin decelerates by thiol compounds and trinitrophenylation, but accelerates by modification of carboxyl groups. Arch Biochem Biophys 1998; 358:164-70. [PMID: 9750177 DOI: 10.1006/abbi.1998.0815] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A disulfide isomerization at the C-terminus of cobrotoxin occurred spontaneously by dissolving in alkali buffer. Irreversible conversion of cobrotoxin into its isomers was completely achieved within 4 days. The isomerization reaction was decelerated by thiol compounds including GSSG, GSH, cystamine, and cysteamine in a pseudo-first-order kinetic, and GSSG was the most effective one among the thiol compounds used. Moreover, the oxidized thiol compounds were always superior to reduced ones in decreasing the rate of disulfide interchange. To further assess the intrinsic elements essential for the occurrence of disulfide isomerization of cobrotoxin, the toxin molecule was subjected to modification on its Arg, Lys, Trp, Tyr, and carboxyl groups. In sharp contrast to other modified derivatives, the isomerization reaction was decelerated by trinitrophenylation on Lys-26, Lys-27, and Lys-47, whereas it was rapidly completed after modification of carboxyl groups. Neither chemical modification nor the toxin's conformation affected the irreversibility of isomerization reaction. Thus, the observed change in the rate of disulfide isomerization reflects the involvement of Lys residues and carboxyl groups in this reaction. Although thiol compounds further decelerated the conversion of trinitrophenylated cobrotoxin into its isomers, they did not exert a notable effect on the isomerization of carboxyl groups-modified derivative. These results clearly indicate that disulfide isomerization of cobrotoxin is, in part, driven by the positively charged Lys residues at positions 26, 27, and 47 of the toxin molecule, and that the thiol compounds are coordinated with the negatively charged groups of cobrotoxin to exert their inhibitory action.
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Affiliation(s)
- L Chang
- Department of Biochemistry, Kaohsiung Medical College, Kaohsiung, 807, Taiwan.
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