Long-distance rotational echo double resonance measurements for the determination of secondary structure and conformational heterogeneity in peptides

The utility of rotational echo double resonance (REDOR) NMR spectroscopy fo r determining the conformations of Linear peptides has been examined critic ally using a series of crystalline and amorphous samples. The focus of the present work was the evaluation of long-distance(> 5 Angstrom) interactions using C-13-N-15 dephasing, Detailed studies of specifically labeled melano statin and synthetic analogs of the alpha-factor yeast mating hormone show that nitrogen-dephased, carbon-observe REDOR measurements are reliable for distances up to 6.0 Angstrom, and that dipolar interactions can be detected for distances up to 7 Angstrom. By contrast, nitrogen-observe REDOR gives reliable results only for distances shorter than 5.0 Angstrom. To measure d istances accurately, REDOR data must be corrected for the effects of natura l-abundance spins. These corrections are particularly important for measuri ng long distances, which are of the greatest value for determining peptide secondary structure. We have developed a spherical shell model for calculat ing the effect of these background spins. The REDOR studies also indicate t hat in a lyophilized powder, the tridecapeptide alpha-factor mating pheromo ne from Saccharomyces cerevisiae (WHWLQLKPGQPMY) probably exists as a distr ibution of different turn structures around the KPGQ region. This finding r evises previous solid-state NMR studies on this peptide, which concluded al pha-factor assumes a distorted type-I beta-turn in the Pro-Gly central regi on of the molecule [J.R. Garbow, M. Breslav, O. Antohi, F. Naider, Biochemi stry, 33 (2994) 10094]. (C) 1999 Elsevier Science B.V. All rights reserved.