Mutations on the N-terminal region abolish differentially the enzymatic activity, membrane-damaging activity and cytotoxicity of Taiwan cobra phospholipase A2

To examine the functional contribution of the N-terminal region to the activities of Naja naja atra phospholipase A2 (PLA2), studies on three N-terminally mutated PLA2 were carried out in the present work. Removal of N-terminal heptapeptide caused a complete loss of membrane-damaging activity, whilst the mutants with an extra Met before Asn-1 or substituting Asn-1 with Met still retained approximately 40.9% and 82.9% membrane-damaging activity of the native enzyme, respectively. Mutations on the N-terminal region did not greatly affect the Ca2+-binding ability but caused a precipitous drop in PLA2 activity. Moreover, the gross conformation of the mutants was different from that of the native enzyme as revealed by CD spectra. Nevertheless, the mutants as well as native PLA2 induced apoptotic death of U937 cells, and the cytotoxicity of mutants was similar to or even greater than that of the native PLA2. These results indicate that mutations on the N-terminus abolish the enzymatic activity, membrane-damaging activity and cytotoxicity of N. naja atra PLA2 in different ways, and suggest a feasible approach to selective elimination of the multiple activities of PLA2 enzymes.