Differential expression and geographic variation of the venom phospholipases A₂ of Calloselasma rhodostoma and Trimeresurus mucrosquamatus

To investigate the geographic variations in venoms of two medically important pitvipers, we have purified and characterized the phospholipases A₂ (PLA₂s) from the pooled venoms of Calloselasma rhodostoma from Malaysia, Thailand, Indonesia, and Vietnam, as well as the individual venom of Trimeresurus mucrosquamatus collected from both North and South Taiwan. Enzymatic and pharmacological activities of the purified PLA₂s were also investigated. The complete amino acid sequences of the purified PLA₂s were determined by sequencing the corresponding cDNAs from the venom gland and shown to be consistent with their molecular weight data and the N-terminal sequences. All the geographic venom samples of C. rhodostoma contain a major noncatalytic basic PLA₂-homolog and two or three acidic PLA₂s in different proportions. These acidic PLA₂s contain Glu6-substitutions and show distinct inhibiting specificities toward the platelets from human and rabbit. We also found that the T. mucrosquamatus venoms from North Taiwan but not those from South Taiwan contain an Arg6-PLA₂ designated as TmPL-III. Its amino acid sequence is reported for the first time. This enzyme is structurally almost identical to the low- or nonexpressed Arg6-PLA₂ from C. rhodostoma venom gland, and thus appears to be a regressing venom component in both of the Asian pitvipers.