Identification and evolution of venom phospholipase A2 inhibitors from Protobothrops elegans serum

Abstract

The cDNAs encoding venom phospholipase A2(PLA2) inhibitors (PLIs), named Protobothrops elegans (Pe)γ-PLI-A, PeγPLI-B, PeαPLI-A, and PeαPLI-B, were cloned from the P. elegans liver cDNA library. They were further divided into several constituents due to nucleotide substitutions in their open reading frames. For PeαPLI-A, two constituents, PeαPLI-Aaand Peα-PLI-Ab, were identified due to three nonsynonymous substitutions in exon 3. Far-western blot and massspectrometry analysis of the P. elegans serum proteins showed the presence of γPLIs, and αPLIs, which can bind venom PLA2s. In αPLIs from Protobothrops sera, A or B subtype-specific amino acid substitutions are concentrated only in exon 3. A comparison of γPLIs showed that γPLI-As are conserved and γPLI-Bs diversified. Mathematical analysis of the nucleotide sequences of Protobothrops γPLI-B cDNAs revealed that the particular loops in the three-finger motifs diversified by accelerated evolution. Such evolutionary features should have made serum PLIs acquire their respective inhibitory activities to adapt to venom PLA2 isozymes.