Elucidation of the solution structure of cardiotoxin analogue V from the Taiwan cobra (Naja naja atra)—Identification of structural features important for the lethal action of snake venom cardiotoxins

Abstract

The aim of the present study is to understand the structural features responsible for the lethal activity of snake venom cardiotoxins. Comparison of the lethal potency of the five cardiotoxin isoforms isolated from the venom of Taiwan cobrã Naja naja atra! reveals that the lethal potency of CTX I and CTX V are about twice of that exhibited by CTX II, CTX III, and CTX IV. In the present study, the solution structure of CTX V has been determined at high resolution using multidimensional proton NMR spectroscopy and dynamical simulated annealing techniques. Comparison of the high resolution solution structures of CTX V with that of CTX IV reveals that the secondary structural elements in both the toxin isoforms consist of a triple and double-stranded antiparallel b-sheet domains. Critical examination of the threedimensional structure of CTX V shows that the residues at the tip of Loop III form a distinct "finger-shaped" projection comprising of nonpolar residues. The occurrence of the nonpolar "finger-shaped" projection leads to the formation of a prominent cleft between the residues located at the tip of Loops II and III. Interestingly, the occurrence of a backbone hydrogen bonding~Val27CO to Leu48NH! in CTX IV is found to distort the "finger-shaped" projection and consequently diminish the cleft formation at the tip of Loops II and III. Comparison of the solution structures and lethal potencies of other cardiotoxin isoforms isolated from the Taiwan cobra~Naja naja atra! venom shows that a strong correlation exists between the lethal potency and occurrence of the nonpolar "finger-shaped" projection at the tip of Loop III. Critical analysis of the structures of the various CTX isoforms from the Taiwan cobra suggest that the degree of exposure of the cationic charge~to the solvent! contributed by the invariant lysine residue at position 44 on the convex side of the CTX molecules could be another crucial factor governing their lethal potency.

Antinociceptive and Anti-Inflammatory Effects of Orally Administrated Denatured Naja Naja Atra Venom on Murine Rheumatoid Arthritis Models

“…Heat treatment (NNAV+) induced an increase in protein contents with about MW 7 KD. According to the literature, the protein band of MW 7 KD contained cardiotoxin and neurotoxin [21, 22]. In contrast, heat treatment did not markedly alter the components of high MW proteins (more than 20 KD) in NNAV.…”

Snake Venom Cytotoxins, Phospholipase A2s, and Zn2+-dependent Metalloproteinases: Mechanisms of Action and Pharmacological Relevance

“…This event leads to formation of pores, whose size and life time have been estimated to be in the range of 30 Å and 10 −2 s respectively [49,50]. Although the precise molecular mechanism of action remains to be elucidated, it is well accepted that basic residues, namely Lys and Arg, are required for the interaction of cytotoxins with negatively charged phospholipids that are located on the outer leaflets of lipid bilayers [51] (Figure 1). While α-neurotoxins (also TF proteins from cobra venom) mainly exert their pathological effects by physically interacting with select protein receptors, no specific protein targets have yet been identified for cytotoxins from cobra venom [29].…”

Structure and Dynamics of Cardiotoxins

“…NTs target different muscle and neuronal nicotinic acetylcholine receptors [4]. So far, no specific protein target was revealed for CTs, although its existence has been offered [5][6][7].…”