SOLUTION STRUCTURES OF NISIN-A AND ITS 2 MAJOR DEGRADATION PRODUCTS DETERMINED BY NMR

The conformations of nisin and two major degradation products, nisin-(1-32)-peptide (nisin1-32) and des-DELTA-Ala5-nisin1-32 (where DELTA-Ala is alpha/beta-didehydroalanine), in aqueous solution have been determined from n.m.r. data. Sequential assignments of the peptides using correlation spectroscopy ('COSY'), homonuclear Hartmann--Hahn spectroscopy ('HOHAHA'), nuclear Overhauser enhancement spectroscopy (NOESY), relayed NOESY and rotating-frame nuclear Overhauser spectroscopy (ROESY) experiments are presented, including stereospecific assignments of beta-methylene protons of the lanthionine residues. ROESY experiments are also used to detect flexible regions in the polypeptide chain. A dynamic-stimulated-annealing approach is used for structural determination. It can bc concluded that all these peptides are flexible in aqueous solution, with no experimental evidence of preferred overall conformations; the only defined conformational features are imposed by the presence of the lanthionine residues. Low-temperature studies also reveal that des-DELTA-Ala5-nisin1-32 adopts conformations similar to those when the ring is intact, suggesting that the loss of activity of this degradation product is due to the absence of the DELTA-Ala5 residue rather than to the conformational consequences of ring-opening.