Identification and characterization of a serum protein homologous to α-type phospholipase A2 inhibitor (PLIα) from a nonvenomous snake, Elaphe quadrivirgata

From a liver cDNA library prepared from a nonvenomous striated snake, Elaphe quadrivirgata , we isolated a cDNA encoding a novel protein, PLIalpha-like protein (PLIalpha-LP), having approximately 70% sequence identities with the alpha-type phospholipase A(2) (PLA(2) ) inhibitors (PLIalphas) previously purified from the venomous snakes Agkistrodon blomhoffii siniticus and Trimeresurus flavoviridis . Since the PLIalpha-LP with a highly conserved C-type lectin-like domain (CTLD) would be predicted to function as a PLA(2) inhibitor, we purified this protein from E. quadrivirgata serum by sequential chromatography on Hi-trap Blue, Mono Q, and Superdex 200 columns. The purified 51-kDa protein with PLIalpha-like immunoreactivity was found to be a trimer of 18-kDa PLIalpha-LP, which was comparable to the trimeric structure of PLIalpha. But, unexpectedly, this protein did not show any inhibitory activity against various snake venom PLA(2)s. Furthermore, it did not inhibit the endogenous PLA(2) activities in various tissue homogenates prepared from this snake. Lack of the inhibitory activity in PLIalpha-LP may provide important information concerning the structure-function relationships of PLIalpha.