Cross-reactivities of monoclonal antibodies to a myotoxin from the venom of the broad-banded copperhead (Agkistrodon contortrix laticinctus)

Lys49 myotoxins, secreted phospholipase A2-like proteins of viperid venoms: A comprehensive review

Muscle necrosis is a potential clinical complication of snakebite envenomings, which in severe cases can lead to functional or physical sequelae such as disability or amputation. Snake venom proteins with the ability to directly damage skeletal muscle fibers are collectively referred to as myotoxins, and include three main types: cytolysins of the "three-finger toxin" protein family expressed in many elapid venoms, the so-called "small" myotoxins found in a number of rattlesnake venoms, and the widespread secreted phospholipase A₂ (sPLA₂) molecules. Among the latter, protein variants that conserve the sPLA₂ structure, but lack such enzymatic activity, have been increasingly found in the venoms of many viperid species. Intriguingly, these sPLA₂-like proteins are able to induce muscle necrosis by a mechanism independent of phospholipid hydrolysis. They are commonly referred to as "Lys49 myotoxins" since they most often present, among other substitutions, the replacement of the otherwise invariant residue Asp49 of sPLA₂s by Lys. This work comprehensively reviews the historical developments and current knowledge towards deciphering the mechanism of action of Lys49 sPLA₂-like myotoxins, and points out main gaps to be filled for a better understanding of these multifaceted snake venom proteins, to hopefully lead to improved treatments for snakebites.

Research strategies to improve snakebite treatment: challenges and progress

Antivenom is an effective treatment of snakebite but, because of the complex interplay of fiscal, epidemiological, therapeutic efficacy and safety issues, the mortality of snakebite remains unacceptably high. Efficiently combating this high level of preventable death amongst the world's most disadvantaged communities requires the globally-coordinated action of multiple intervention programmes. This is the overall objective of the Global Snakebite Initiative. This paper describes the challenges facing the research community to develop snakebite treatments that are more efficacious, safe and affordable than current therapy.

Lysine 49 phospholipase A2 proteins

The structures of several K49 PLA2 proteins have been determined and these differ as a group in several regions from the closely related D49 PLA2 enzymes. One outstanding difference is the presence of a high number of positively charged residues in the C-terminal region which combined with the overall high number of conserved lysine residues gives the molecule an interfacial adsorption surface which is highly positively charged compared to the opposite surface of the molecule. Although some nucleotide sequences have been reported, progress in obtaining active recombinant proteins has been slow. The K49 proteins exert several toxic activities, including myotoxicity, anticoagulation and edema formation. The most studied of these activities is myotoxicity. The myotoxicity induced by the K49 PLA2 proteins is histologically similar to that caused by the D49 PLA2 myotoxins, with some muscle fiber types possibly more sensitive than others. Whereas it is clear that the K49 PLA2 myotoxins lyse the plasma membrane of the affected muscle cell in vivo, the exact mechanism of this lysis is not known. Also, it is not known whether the toxin is internalized before, during or after the initial lysis or ever. The K49 PLA2 toxins lyse liposomes and cells in culture and in the latter, the PLA2 myotoxins exert at least two distinct mechanisms of action, neither of which is well-characterized. While the K49 PLA2 proteins are enzymatically inactive on artificial substrates, the toxins cause fatty acid production in cell cultures. Whether the fatty acid release is due to the enzymatic activity of the K49 PLA2 or stimulation of tissue lipases, is unknown. While there may be a role for fatty acid production in one mechanism of myotoxicity, a second mechanism appears to be independent of enzymatic activity. Although we are beginning to understand more about the structure of these toxins, we still know little about the precise mechanism by which they interact with the skeletal muscle cell in vivo.

Development of an enzyme-linked immunosorbent assay (ELISA) for identification of venoms from snakes in the Agkistrodon genus

An enzyme-linked immunosorbent assay (ELISA) using a purified myotoxin from the venom of Agkistrodon contortrix laticintus (broad-banded copperhead) as immunogen was developed for potential use in the identification of envenomation by snakes belonging to the genus Agkistrodon native to North America. The specificity of the assay was tested using a total of 43 venom samples from snakes of diverse geographic locations. Venom samples used for cross-reactivity determination represent eight snake families including 14 species from the genus Crotalus. The assay detected venom from all Agkistrodon species tested without significant cross-reactivity with other venoms except for samples from two species of Bothrops which do not occur naturally north of Southern Mexico. The detection limit of the assay was 2 ng/ml for homologous crude venom dissolved in normal human serum. The assay was highly accurate in correlating optical densities with venom concentrations (r = 0.997). The presence of the antigen in experimental envenomations was readily detected by the assay at an i.m. injection dosage of 0.1 microgram/g. This ELISA is a promising test for identification of envenomations by species of Agkistrodon found in most of North America. It can also be used to study the kinetics of the myotoxin in experimental envenomations.