CONFORMATIONAL-ANALYSIS OF THE SACCHAROMYCES-CEREVISIAE TRIDECAPEPTIDE MATING PHEROMONE BY C-13, N-15 ROTATIONAL-ECHO DOUBLE-RESONANCE NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

The solid-state conformation of [Nle(12)]alpha-factor, the Saccharomyces cerevisiae tridecapeptide mating pheromone (WHWLQLKPGQPNleY), was investigated by C-13,N-15 rotational-echo double resonance (REDOR) nuclear magnetic resonance spectroscopy (NMR). Previous high-resolution NMR studies of [Nle(12)]alpha-factor in solution revealed a transient Type II beta-turn spanning residues 7-10 of the peptide. To investigate this region of [Nle(12)]alpha-factor in the solid state, a series of four selectively C-13,N-15-enriched tridecapeptides were synthesized by solid-phase methods. Carbon-nitrogen distances between the labeled sites in lyophilized samples of [Nle(12)]alpha-factor were accurately measured by REDOR NMR. Experimentally determined distances were compared with those from calculated models for Type I and Type II beta-turns and for an extended chain. The measured distances indicate that, in a lyophilized powder, the central region of the [Nle(12)]alpha-factor is not in an extended conformation. The experimental data was most consistent with distances obtained from a distorted Type I beta-turn model.