Structure and phylogeny of the venom group I phospholipase A(2) gene

Phospholipases A(2) (PLA(2)s) catalyzing the hydrolysis of phospholipids fo rm a family of proteins with diverse physiological and pharmacological prop erties. While there have been several reports on the cloning of PLA(2) cDNA s, very few studies have been carried out on the PLA(2) genes and, most imp ortantly, no information has been available on the gene structure and funct ion of group I venom PLA(2). This study, on the PLA(2) gene from a spitting cobra, besides being the very first report on any venom group I PLA(2) gen e, constitutes the missing link in the biology and evolution of phospholipa ses. The 4-kb gene consists of four exons and three introns and resembles t he human pancreatic PLA(2) gene. However, the size of intron 3 in particula r is much smaller than that in the pancreatic gene. Interestingly, the info rmation for the toxic and most of the pharmacological properties of the ven om PLA(2) can be attributed to the end of exon 3 and the whole of exon 4 of the gene. This functional delineation fits in well with the theory of adap tive evolution exhibited by the venom PLA(2)s. We also show that the mammal ian pancreatic and elapid PLA(2)s have similar paths of evolution (probably following gene duplication) from a common ancestral gene. Venom group II p hospholipases, although evolved from the same ancestor, diverged early in e volution from the group I PLA(2) genes. Intriguingly, CAT reporter gene ass ays and DNase 1 footprinting studies on the promoter and its deletion const ructs using CHO and HepG2 cell lines identified the possible involvement of cis elements such as Sp1, AP2, gamma-IRE, and (TG)(12) repeats in the expr ession of the gene in a tissue-specific manner