Multiplicity of acidic subunit isoforms of crotoxin, the phospholipase A2 neurotoxin from Crotalus durissus terrificus venom, results from posttranslational modifications

Abstract

Crotoxin, the major toxin of the venom of the South American rattlesnake, Crotalus durissus terrificus, is made of two subunits: component B, a basic and weakly toxic phospholipase A2, and component A, an acidic and nontoxic protein that enhances the lethal potency of component B. Crotoxin is a mixture of isoforms that results from the association of several isoforms of its two subunits. In the present investigation, we have purified four component A isoforms that, when associated with the same purified component B isoform, produced different crotoxin isoforms, all having the same specific enzymatic activity and the same lethal potency. We further determined by Edman degradation the polypeptide sequences of these four component A isoforms. They are made of three disulfide-linked polypeptide chains (alpha, beta, and gamma) that correspond to three different regions of a phospholipase A2 precursor. We observed that the polypeptide sequences of the various component A isoforms all agree with the sequence of an unique precursor. The differences between the isoforms result first by differences in the length of the various chains alpha and beta, indicating that component A isoforms are generated from the proteolytic cleavage of the component A precursor at very close sites, possibly by the combined actions of endopeptidases and exopeptidases, and second by the possible cyclization of the alpha-NH2 of the N-terminal glutamine residue of chains beta and gamma. These observations indicate that the component A isoforms are the consequence of different posttranslational events occurring on an unique precursor, rather than the expression of different genes.

Renal and vascular effects of Crotalus durissus cumanensis venom and its crotoxin fraction

“…Interestingly, Crpt possesses anti-inflammatory activity in vivo, possibly because it interacts with extracellular PLA 2 generated during the inflammatory process (33). There are several crotoxin isoforms that may result from a random association between PLA 2 and Crpt (34). This multiplicity and diversity of crotoxin isoforms appear to result from either a post-translational modification of a unique precursor of crotoxin or expression of different mRNA (35).…”

Biological and Structural Characterization of Crotoxin and New Isoform of Crotoxin B PLA2 (F6a) from Crotalus durissus collilineatus Snake Venom

“…These findings suggested that the crotoxin isoforms from Crotalus durissus collilineatus probably plays an important role in this venomÕs action (Ponce-Soto, 2002). Several studies have shown that the venom of Crotalus durissus terrificus contains various isoforms of PLA 2 Bon, 1987, 1988;Faure, 1991Faure, , 1993Faure, , 1994. In this work, we describe the biochemical and pharmacological characterization of a new crotoxin B isoform PLA 2 (F6a) of crotoxin B from Crotalus durissus collilineatus.…”

“…Crotoxin exists in several isoforms, which vary in their biological activity, probably as a result of the heterogeneity in the PLA 2 and crotapotins (Faure and Bon, 1987). The multiplicity and diversity of crotoxin isoforms may be due to post-translational modification of a unique precursor of crotoxin or from the expression of different mRNAs Bon, 1987, 1988;Faure, 1991Faure, , 1993Faure, , 1994.…”

The Anticoagulant Effect of the Human Secretory Phospholipase A2 on Blood Plasma and on a Cell‐Free System is Due to a Phospholipid‐Independent Mechanism of Action Involving the Inhibition of Factor Va

“…The CB subunit of crotoxin (group 11) was purified from Crotalus durissus terrificus venom, as previously described (Faure et al, 1991). Bovine and porcine pancreatic PLA, (group I) were from Sigma and from Boehringer (Mannheim), respectively.…”