Isolation and amino acid sequence of a phospholipase A2 inhibitor from the blood plasma of the sea krait, Laticauda semifasciata.

Abstract

A phospholipase A2 (PLA2) inhibitor was purified from the blood plasma of a sea krait, Laticauda semifasciata, by sequential chromatography on Sephadex G-200, Mono Q, and Phenyl Sepharose columns. The purified inhibitor was found to be the same type as the PLA2 inhibitors, named PLIgamma, that had been purified from the blood plasma of the Thai cobra Naja naja kaouthia [Ohkura et al. (1994) Biochem. Biophys. Res. Commun. 200, 784-788] and Chinese mamushi Agkistrodon blomhoffii siniticus [Ohkura et al. (1997) Biochem. J. 325, 527-531]. Like other PLIgammas, the L. semifasciata inhibitor (LsPLIgamma) inhibited equally all of the PLA2s investigated including Elapid venom PLA2s (group I), Crotalid and Viperid venom PLA2s (group II), and honeybee PLA2 (group III). The LsPLIgamma was a 100-kDa glycoprotein composed of two distinct subunits, LsPLIgamma-A and LsPLIgamma-B, with an approximate molar ratio of 2:1. The amino acid sequences of the two subunits were determined by alignment of the peptides obtained by lysyl endopeptidase, endoproteinase Asp-N, and staphylococcal V8 protease digestions. LsPLIgamma-A and LsPLIgamma-B were composed of 182 and 181 amino acid residues, respectively; and the former subunit was a glycoprotein containing one asparagine-linked sugar chain at the position 157. The sequences of LsPLIgamma-A and LsPLIgamma-B showed 65 and 74% homology, respectively, to those of the corresponding subunits of N. naja kaouthia PLIgamma, and had two tandem patterns of cysteine residues, characteristic of the urokinase-type plasminogen activator receptor (uPAR) and members of the Ly-6 superfamily.