1H, 15N and 13C resonance assignments and secondary structure of group II phospholipase A2 from Agkistrodon piscivorus piscivorus: presence of an amino-terminal helix in solution.

1H, 15N and 13C resonance assignments are presented for the group II phospholipase A2 (PLA2) from Agkistrodon piscivorus piscivorus. The secondary structure of the enzyme has been inferred from an analysis of coupling constants, interproton distances, chemical shifts, and kinetics of amide exchange. Overall, the secondary structure of this PLA2 is similar to the crystal structure of the homologous group II human nonpancreatic secretory phospholipase [Scott, D.L., White, S.P., Browning, J.L., Rosa, J.J., Gelb, M.H. and Sigler, P.B. (1991) Science, 254, 1007-1010]. In the group I enzyme from porcine pancreas, the amino-terminal helix becomes fully ordered in the ternary complex of enzyme, lipid micelles and inhibitor. The formation of this helix is thought to be important for the increase in activity of phospholipases on aggregated substrates [Van den Berg, B., Tessari, M., Boelens, R., Dijkman, R., De Haas, G. H., Kaptein, R. and Verheij, H.M. (1995) Nature Strct. Biol., 2, 402-406]. However, the group II enzyme from Agkistrodon piscivorus piscivorus possesses a defined and well-positioned amino-terminal helix in the absence of substrate. Therefore, there is a clear difference between the conformation group I and group II enzymes in solution. These conformational differences suggest that formation of the amino-terminal helix is a necessary, but not sufficient, step in interfacial activation of phospholipases.