Proton NMR Assignments and Secondary Structure of the Snake Venom Protein Echistatin

Abstract

The snake venom protein echistatin is a potent inhibitor of platelet aggregation. The inhibitory properties of echistatin have been attributed to the Arg-Gly-Asp sequence at residues 24-26. In this paper, sequence-specific nuclear magnetic resonance assignments are presented for the proton resonances of echistatin in water. The single-chain protein contains 49 amino acids and 4 cystine bridges. All of the backbone amide, CαH, and side-chain resonances, except for the η-NH of the arginines, have been assigned. The secondary structure of the protein was characterized from the pattern of nuclear Overhauser enhancements, from the identification of slowly exchanging amide protons, from 3JCαH-NH coupling constants, and from circular dichroism studies. The data suggest that the secondary structure consists of a type I β-turn, a short β-hairpin, and a short, irregular, antiparallel β-sheet and that the Arg-Gly-Asp sequence is in a flexible loop connecting two strands of the distorted antiparallel β-sheet. © 1991, American Chemical Society. All rights reserved.