Amino acid sequence of phospholipase A2-alpha from the venom of Crotalus adamanteus. A new classification of phospholipases A2 based upon structural determinants.

The complete amino acid sequence of Crotalus adamanteus venom phospholipase A2-alpha has been determined by analysis of the five tryptic peptides from the citraconylated, reduced, and S-[14C]carboxamidomethylated enzyme. Earlier studies (Tsao, F. H. C., Keim, P. S., and Heinrikson, R. L. (1975) Arch. Biochem. Biophys. 167, 706) provided the information necessary to align the tryptic fragments so that secondary cleavage procedures to establish overlaps were unnecessary. The subunit in the phospholipase A2-alpha dimer is a single polypeptide chain containing 122 amino acids and seven disulfide bonds. The histidine residue implicated in the active site of mammalian phospholipases is at position 47 in the C. adamanteus enzyme and is located in a domain of the molecule which is highly homologous in sequence with corresponding regions of phospholipases from a variety of venom and pancreatic sources. Comparative sequence analysis has revealed insights with regard to the function and evolution of phospholipases A2. Primary structural relationships observed among the snake venom enzymes parallel the phylogenetic classification of the venomous reptiles from which they were derived. It is proposed that phospholipases A2 of this general type be divided into two groups depending upon the presence or absence of distinctive structural features elucidated in this study.