MULTIPLE CONFORMATION OF THE SEA-ANEMONE POLYPEPTIDE ANTHOPLEURIN-A IN SOLUTION

Anthopleurin-A (AP-A) is a member of a family of sea anemone-derived p olypeptides that interact with sodium channels in a voltage-dependent manner, producing a positive inotropic effect on the mammalian heart. There has been considerable interest in this molecule as a lead compou nd for the development of novel therapeutic agents. Earlier attempts t o define the 3-dimensional structure of AP-A were complicated by the f act that it was found to exist in 2 conformations in solution. Using H -1- and C-13-NMR spectroscopy, we have now shown that this conformatio nal heterogeneity arises from cis-trans isomerization about the Gly 40 -Pro 41 peptide bond and that in the major form of the protein this pe ptide bond adopts a cis conformation. Furthermore, the increased sensi tivity afforded by higher-field NMR has allowed identification of addi tional minor conformations of AP-A, the origin of which is presently u nknown. We believe there will be many more examples of the detection b y high-field NMR of previously unobserved minor conformations of prote ins in solution.