Conformational Analysis of the Saccharomyces cerevisiae Tridecapeptide Mating Pheromone by ¹³C,¹⁵N Rotational-Echo Double Resonance Nuclear Magnetic Resonance Spectroscopy

The solid-state conformation of [Nle¹²]α-factor, the Saccharomyces cerevisiae tridecapeptide mating pheromone (WHWLQLKPGQPNleY), was investigated by ¹³C,¹⁵N rotational-echo double resonance (REDOR) nuclear magnetic resonance spectroscopy (NMR). Previous high-resolution NMR studies of [Nle¹²]α-factor in solution revealed a transient Type II β-turn spanning residues 7–10 of the peptide. To investigate this region of [Nle¹²]α-factor in the solid state, a series of four selectively ¹³C,¹⁵N-enriched tridecapeptides were synthesized by solid-phase methods. Carbon-nitrogen distances between the labeled sites in lyophilized samples of [Nle¹²]α-factor were accurately measured by REDOR NMR. Experimentally determined distances were compared with those from calculated models for Type I and Type II β-turns and for an extended chain. The measured distances indicate that, in a lyophilized powder, the central region of the [Nle¹²]α-factor is not in an extended conformation. The experimental data was most consistent with distances obtained from a distorted Type I β-turn model.