Amphipathic control of the 3(10)-/alpha-helix equilibrium in synthetic peptides.

A series of short, amphipathic peptides incorporating 80% C(alpha),C(alpha)-disubstituted glycines has been prepared to investigate amphipathicity as a helix-stabilizing effect. The peptides were designed to adopt 3(10)- or alpha-helices based on amphipathic design of the primary sequence. Characterization by circular dichroism spectroscopy in various media (1 : 1 acetonitrile/water; 9 : 1 acetonitrile/water; 9 : 1 acetonitrile/TFE; 25 mM SDS micelles in water) indicates that the peptides selectively adopt their designed conformation in micellar environments. We speculate that steric effects from ith and ith + 3 residues interactions may destabilize the 3(10)-helix in peptides containing amino acids with large side-chains, as with 1-aminocyclohexane-1-carboxylic acid (Ac(6)c). This problem may be overcome by alternating large and small amino acids in the ith and ith + 3 residues, which are staggered in the 3(10)-helix.