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Toxins 2019, 11(1), 52; https://doi.org/10.3390/toxins11010052

Monitoring the Disulfide Bonds of Folding Isomers of Synthetic CTX A3 Polypeptide Using MS-Based Technology

1
Mithra Biotechnology Inc., New Taipei City 221, Taiwan
2
Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan
3
College of Life Sciences, National Tsing Hua University, Hsinchu 30013, Taiwan
4
National Health Research Institutes, National Institute of Infectious Diseases and Vaccinology, Miaoli 35053, Taiwan
Both authors contribute equally to this work.
*
Authors to whom correspondence should be addressed.
Received: 29 November 2018 / Revised: 15 January 2019 / Accepted: 15 January 2019 / Published: 17 January 2019
(This article belongs to the Section Animal Venoms)
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Abstract

Native disulfide formation is crucial to the process of disulfide-rich protein folding in vitro. As such, analysis of the disulfide bonds can be used to track the process of the folding reaction; however, the diverse structural isomers interfere with characterization due to the non-native disulfide linkages. Previously, a mass spectrometry (MS) based platform coupled with peptide dimethylation and an automatic disulfide bond searching engine demonstrated the potential to screen disulfide-linked peptides for the unambiguous assignment of paired cysteine residues of toxin components in cobra venom. The developed MS-based platform was evaluated to analyze the disulfide bonds of structural isomers during the folding reaction of synthetic cardiotoxin A3 polypeptide (syn-CTX A3), an important medical component in cobra venom. Through application of this work flow, a total of 13 disulfide-linked peptides were repeatedly identified across the folding reaction, and two of them were found to contain cysteine pairings, like those found in native CTX A3. Quantitative analysis of these disulfide-linked peptides showed the occurrence of a progressive disulfide rearrangement that generates a native disulfide bond pattern on syn-CTX A3 folded protein. The formation of these syn-CTX A3 folded protein reaches a steady level in the late stage of the folding reaction. Biophysical and cell-based assays showed that the collected syn-CTX A3 folded protein have a β-sheet secondary structure and cytotoxic activity similar to that of native CTX A3. In addition, the immunization of the syn-CTX A3 folded proteins could induce neutralization antibodies against the cytotoxic activity of native CTX A3. In contrast, these structure activities were poorly observed in the other folded isomers with non-native disulfide bonds. The study highlights the ability of the developed MS platform to assay isomers with heterogeneous disulfide bonds, providing insight into the folding mechanism of the bioactive protein generation. View Full-Text
Keywords: disulfide bond analysis; folding isomer; cardiotoxin; mass spectrometry disulfide bond analysis; folding isomer; cardiotoxin; mass spectrometry
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    Description: The following are available online at www.mdpi.com/link, Figure S1. Amino acid sequence of synthetic polypeptide with an amidated C-terminal asparagine residue. The solid line linkage between cysteine residues represents the native disulfide bonds found in the native CTX A3 toxin. The bottom line indicates the tryptic fragment linked by these disulfide bonds; Figure S2: The cytotoxic activity of native CTX A3 toxin on the HL-60 cells. Results were acquired from experiments performed in triplicate. The dashed line indicates the toxin concentration that caused death of half of the cells.
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Huang, S.-Y.; Wei, T.-Y.; Liu, B.-S.; Lin, M.-H.; Chiang, S.-K.; Chen, S.-F.; Sung, W.-C. Monitoring the Disulfide Bonds of Folding Isomers of Synthetic CTX A3 Polypeptide Using MS-Based Technology. Toxins 2019, 11, 52.

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