ROLE OF MODIFIED GLUTAMIC-ACID IN THE HELICAL STRUCTURE OF CONANTOKIN-T

Circular dichroism (CD) and 2-dimensional NMR were used to study the s olution conformation of conantokin-T (Con-T), a small peptide toxin fo und in the venom of fish-hunting cone snails, and its Glu-substituted analog, Con-T lacks disulfide bonds but contains many gamma-carboxyglu tamic acids (Gla), a posttranslationally modified residue, Our results show that Con-T adopts an alpha-helical conformation in aqueous solut ion even in the absence of calcium, Glu replacements diminish both hel icity and function of Con-T. The helical content of Con-T is higher th an most natural helical peptides of this length in aqueous solution, T he sequence of this small toxin incorporates several known elements th at stabilize alpha-helical structure in peptides, Gla residues form se veral salt bridges that stabilize helical conformation of Con-T. (C) 1 997 Federation of European Biochemical Societies.