Roles of lysine-69 in dimerization and activity of trimeresurus flavoviridis venom aspartate-49-phospholipase A₂

Trimeresurus flavoviridis (Habu snake) venom aspartate-49-phospholipase A₂ (Asp-49-PLA₂) was reacted at pH 9.0 with a 2-fold molar excess of 2,4,6-trinitrobenzenesulfonate in the absence of Ca²⁺ and two trinitrophenylated derivatives were isolated by HPLC. One was a derivative modified at Lys-11 and its activity was mostly retained. The other was a derivative modified at both Lys-11 and Lys-72 and its activity was 40% that of unmodified enzyme. Trinitrophenylation of Lys-72 appeared to bring about a conformational disorder at the lipid-water interface recognition site and thus a reduction of activity. When the enzyme was modified in the presence of Ca²⁺, activity decreased at a rate much faster than that in the absence of Ca²⁺ and Lys-69 came to be modified. These results suggested that conformational displacement of Asp-49-PLA₂ of a local to global type occurs upon the binding of Ca²⁺. The derivative modified at Lys-69 had 28% activity and existed as a monomer. This supports a previous assumption that Lys-69 participates in dimerization of group II Asp-49-PLA₂s [Brunie et al. (1985) J. Biol. Chem. 260, 9742-9749] and shows that dimerization is not necessarily essential for activity manifestation.