NMR Studies of Lantibiotics: The Three-Dimensional Structure of Nisin in Aqueous Solution

Abstract

Nisin, a bacteriocin produced by Lactococcus lactis ssp., is a post-translationally modified pentacyclic polypeptide of 34 amino acids. It is a member of the class of bacteriocins, known as lantibiotics, that contain the unusual amino acid lanthionine. Its structure in aqueous solution has been determined on the basis of data obtained from Nuclear Magnetic Resonance Spectroscopy (NMR) studies. Translation of the interproton distance constraints, derived from Nuclear Overhauser Enhancement Spectroscopy (NOESY)l, and torsion angle constraints, derived from Double Quantum Filtered Correlated Spectroscopy (DQF-COSY), into a 3D structure was carried out with the distance geometry program DISMAN, followed by restrained energy minimization using CHARMm. Due to the internal mobility of the polypeptide chain a determination of the precise overal folding of the molecule was prohibited, but parts of the structure could be obtained albeit with sometimes low resolution. The structure of nisin can best be described as follows: the outermost N-and C-terminal regions appear quite flexible, the remainder of the molecule consists of an amphiphilic N-terminal fragment (residues 3–19), joined by a flexible ‘hinge’ region to a rigid doublering fragment formed by residues 23–28. The latter fragment has the appearance of a somewhat overwound α-helix. It is postulated that i) the coupling between residues 23 and 26 as well as between 25 and 28 by thioether bridges and ii) the inversion of the Cα chiralities at positions 23 and 25 occurs via an intermediate α-helical structure of the prenisin molecule