Prev. Article Next Article Table of Contents

Article

Investigation of the Structural Stability of Cardiotoxin Analogue III from the Taiwan Cobra by Hydrogen−Deuterium Exchange Kinetics^†

Thirunavukkarasu Sivaraman, Thallampuranam Krishnaswamy S. Kumar, and Chin Yu*

Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan

Biochemistry, 1999, 38 (31), pp 9899–9905

DOI: 10.1021/bi9901230

Publication Date (Web): July 16, 1999

†

This work was supported by the National Science Council, Taiwan (NSC 88-2311-B-007-021 and NSC 88-2113-M-007-028) and Dr. C. S. Tsong Memorial Medical Research Foundation (VGHTH-87-09-2).

To whom correspondence should be addressed: Fax +886 35 711082; E-mail cyu@chem.nthu.edu.tw.

Abstract

The conformational stability of a small (7 kDa), all β-sheet protein, cardiotoxin analogue III (CTX III), from the venom of the Taiwan cobra has been investigated by hydrogen−deuterium (H/D) exchange using two-dimensional NMR spectroscopy. The H/D exchange kinetics of backbone amide protons in CTX III has been monitored at pD 3.6 and 6.6 (at 25 °C), for over 5000 h. Examination of H/D exchange kinetics in the protein showed that a number of slowly exchanging residues are in the hydrophobic core of the protein. The average protection factor of the amide protons of residues belonging to the triple-stranded β-sheet domain is about 20 times greater than that of those in the double-stranded β-sheet segment. The residues in the C-terminal tail of the molecule, though structureless, have been found to exhibit significant protection against H/D exchange. Comparison of the quenched-flow H/D exchange data on CTX III with those obtained in the present study reveals that the most slowly exchanging portion constitutes the folding core of the protein.