Purification, characterization and cDNA cloning of a phospholipase A2 inhibitor from the serum of the non-venomous snake Elaphe quadrivirgata.

The serum of a non-venomous striated snake, Elaphe quadrivirgata, was found to contain phospholipase A2 (PLA2) inhibitory proteins (PLIs). One of these inhibitors was purified by Sephadex G-200 gel filtration, Q-Sepharose FF ion-exchange chromatography and Butyl Sepharose 4FF hydrophobic chromatography. The purified PLI inhibited the enzymic activities of all PLA2 groups, including Elapidae venom (group-I), Viperidae venom (group-II) and honeybee PLA2s (group-III). The inhibitor was a 130 kDa glycoprotein consisting of two distinct subunits, A and B, of 30 and 29 kDa respectively; each of which was glycosylated with N-linked oligosaccharide chains. The cDNAs encoding the respective inhibitor subunits were isolated from a liver cDNA library by the use of probes, prepared by PCR, based on the partially determined amino-acid sequences of the corresponding subunits. The respective nucleotide sequences encoded 19-amino-acid-residue signal sequences, followed by 183- and 181-residue protein sequences for the A and B subunits respectively. The amino-acid sequences revealed that the E. quadrivirgata inhibitor corresponded to PLIgamma, one of three kinds of inhibitors purified from venomous snakes. The existence of PLIgamma in the serum of this non-venomous snake suggested that, besides having a protective role against the venom PLA2s of other venomous snakes, PLIgamma has other important physiological functions in regulating local PLA2 activities; and thus it raises the possibility that PLIgamma occurs in other animals, including mammals.