Biochemical characterization of phospholipase A2 (trimorphin) from the venom of the Sonoran Lyre Snake Trimorphodon biscutatus lambda (family Colubridae).

Phospholipases A(2) (PLA(2)), common venom components and bioregulatory enzymes, have been isolated and sequenced from many snake venoms, but never from the venom (Duvernoy's gland secretion) of colubrid snakes. We report for the first time the purification, biochemical characterization and partial sequence of a PLA(2) (trimorphin) from the venom of a colubrid snake, Trimorphodon biscutatus lambda (Sonoran Lyre Snake). Specific phospholipase activity of the purified PLA(2) was confirmed by enzyme assays. The molecular weight of the enzyme has been determined by SDS-PAGE and mass spectrometry to be 13,996 kDa. The sequence of 50 amino acid residues from the N-terminal has been identified and shows a high degree of sequence homology to the type IA PLA(2)s, especially the Asp-49 enzymes. The Cys-11 residue, characteristic of the group IA PLA(2)s, and the Ca(2+) binding loop residues (Tyr-28, Gly-30, Gly-32, and Asp-49) are conserved. In addition, the His-48 residue, a key component of the active site, is also conserved in trimorphin. The results of phylogenetic analysis on the basis of amino acid sequence homology demonstrate that trimorphin belongs to the type IA family, and it appears to share a close evolutionary relationship with the PLA(2)s from hydrophiine elapid snakes (sea snakes and Australian venomous snakes).