Glycan structures and intrageneric variations of venom acidic phospholipases A2 from Tropidolaemus pitvipers

Most of the phospholipases A2 (PLA2; EC3.1.1.4) variants isolated so far from snake venoms are nonglycosylated enzymes. In the present study, we purified an active glycosylated PLA2 and an inactive nonglycosylated Lys49-like PLA2 from two geographical venom samples of Tropidolaemus. The PLA2 variants from the two samples have rather different N-terminal sequences, implying that the samples were probably derived from two species (Tropidolaemus subannulatus and Tropidolaemus wagleri). The active PLA2s from Sulawesi and Sumatra venoms were designated as Tsu-E6 and Twa-E6, respectively, as a result of the presence of their conserved Glu6 residue. Tsu-E6 inhibited ADP-induced aggregation of mouse and human platelets. Twa-E6 stimulated the aggregation of mouse platelets but inhibited the aggregation of human platelets. Both PLA2s were found to be glycosylated at Asn14. Using MALDI-TOF analysis, the released glycans were shown to comprise complex type oligosaccharides without sialylation. This is the first glycan structure of the snake venom PLA2 to be solved. Furthermore, the enzymatic removal of glycans from both PLA2s did not significantly alter their effects on lipid hydrolysis and platelet aggregation. The thermostability of glycosylated Twa-E6 was also found to be as good as that of other homologous PLA2s. The presence of these oligosaccharides in PLA2s warrants further analyses, which may provide useful insights into the functional regulation of these biomolecules.