Structural Characteristics and Evolution of a Novel Venom Phospholipase A₂ Gene from Protobothrops flavoviridis

Abstract

A novel phospholipase A₂ (PLA₂) gene, named PfPLA 6, was found in a 6,328-bp NIS-1(5′)-a segment in the Protobothrops flavoviridis (Habu, Crotalinae) genome. A comparison of the aligned nucleotide sequences of Viperidae (Viperinae and Crotalinae) venom PLA₂ genes, including PfPLA 6, revealed the deletion of a 12-bp segment called S1EX 1 and a 55-bp segment called S2EX 1 in exon 1 and the interposition of a 219-bp segment called SINT 2 (SINE) in intron 2. A classification of Viperidae PLA₂ genes based on these structural modes indicated that the A-type genes (without SINE), including PfPLA 6, are evolutionarily ancestral to the B-type (Viperinae) and C-type (Crotalinae) PLA₂ genes (both with SINE). Since PfPLA 6 is a pseudogene, an active prototype of PfPLA 6 can be assumed to be the ancestral PLA₂ gene. Putative evolutionary processes from this A-type prototype PLA₂ gene to descendent PLA₂ genes are discussed.