Structure, dynamics, and topological orientation of the polyether, ionophore antibiotic monensin, in a micellar environment.

The structure and dynamics of the ionophoric antibiotic monensin in the presence of micelles have been determined. The conformation of monensin was derived from 50 nuclear Overhauser enhancement (NOE) derived distance restraints and metric-matrix based distance geometry calculations. The conformation was further refined with extensive NOE restrained molecular dynamics simulations carried out in a biphasic simulation cell. From the addition of doxylstearate and monitoring of the induced relaxation of the nmr signals, the relative topological orientation of the molecule within the micelle was ascertained. The results indicate two dihedral angles that act as hinge regions allowing the molecule to adopt a wide range of conformations. Considering the biological activity of monensin, i.e., the capture and transport of cations across cell membranes, an open and closed form of monensin have been postulated. The identification of these hinge regions, which are only observed in the membrane-like environment of the detergent micelles, provides insight into the mechanism of action and can serve as targets for modification to alter the biological profile of monensin.