Contribution of enzymatic activity and receptorbinding to the neurotoxic effects of OS2 on the chick biventer cervicis nerve-muscle preparation. 

Rash, L.D.; Rouault, M.; Lazdunski, M. and Lambeau, G. 

Institut de Pharmacologie Moleculaire et Cellulaire – CNRS. Sophia Antipolis, 660 Route des Lucioles, Valbonne 06560, France.

Snake venom secreted phospholipases A2 (sPLA2s) are part of a growing family of enzymes that catalyse the hydrolysis of phospholipids to release free fattty acids and lysophospholipids. These enzymes exert a wide variety of pharmacological activities including neurotoxicity, myotoxicity and cardiotoxicity. The structure-function relationships of sPLA2s are complex. In addition to the enzyme active site, two high affinity binding sites (N and M) for sPLA2s have been identified using the neurotoxic sPLA2 OS2 isolated from the venom of the Australian taipan (O. scutellatus). The current study used recombinant OS2, OS1 (homologous to OS2 but does not bind to N receptors) and a series of mutants and chimeras of OS2 and OS1, with various combinations of enzymatic activity and binding affinities along with bee venom PLA2 and basic PLA2 from Najamossambica to examine the effect of these properties on in vitro neurotoxicity. In vitro neurotoxicity was assessed using the indirectly-stimulated, chick isolated biventer cervicis nerve-muscle preparation. OS2, mutant OS2 K31L-R34S, bee venom PLA2 and N. mossambica PLA2, which all possess enzymatic activity and high affinity for the N receptor, caused time-dependent decreases in twitch height. Conversely, OS1 and mutants and chimeras which lack enzymatic activity, affinity for the N receptor or both all had no effect on indirectly evoked twitches. These results suggest that both affinity for the N receptor for sPLA2s and hydrolytic activity are required for presynaptic neurotoxicity at the neuromuscular junction.

Support : CNRS, INSERM / NH&MRC.

Correspondence to: rash@ipmc.cnrs.fr