PROTEIN AND CDNA STRUCTURES OF AN ACIDIC PHOSPHOLIPASE-A(2), THE ENZYMATIC PART OF AN UNUSUAL, 2-COMPONENT TOXIN FROM VIPERA-PALAESTINAE

In the venom of Vipera palaestinae an unusual, two-component toxin was found. The two components of the toxin are an acidic phospholipase A( 2) (VpaPLA(2)) and a basic protein, both with an apparent molecular ma ss of about 15 kDa. Each component alone is not toxic; however, their mixture is lethal. We have determined the amino acid and cDNA sequence s of VpaPLA(2). The protein primary structure was solved by sequencing the peptides generated by chemical cleavage of the molecule using CNB r, formic acid and hydroxylamine-hydrochloride and by enzymatic fragme ntation with trypsin and chymotrypsin. VpaPLA(2) consists of 122 amino acid residues and has all the structural characteristics of subgroup IIA PLA(2)s. It shows the highest amino acid similarity to a non-toxic phospholipase A(2) from Eristocophis macmahoni (82%), whereas the mos t similar toxic phospholipases A(2) share about 70% of residues with V paPLA(2). The substitution of His20 for a hydrophobic residue (Leu) in VpaPLA(2) might be one of the reasons that its complex with the basic protein could not be observed. (C) 1996 Academic Press, Inc.