Crystal structure of cytochrome P450 NysL and the structural basis for stereo- and regio-selective oxidation of antifungal macrolides.

NysL, a cytochrome P450 monooxygenase from the Gram-positive bacterium Streptomyces noursei, catalyzes the C10 hydroxylation of 10-deoxynystain to nystatin A1, a clinically important antifungal. In this study, we present the 2.0 Å resolution crystal structure of NysL bound to nystatin A1. The structure of this complex provides key insights into the structural elements that dictate the regio- and stereo-selective oxidation of large 20-44-membered macrolide substrates. The closely related AmphL operates on a similar 38-member macrolide but oxidizes C8 rather than C10. This difference requires that the substrate for AmphL penetrate further into the active site relative to NysL. The depth of substrate penetration is controlled by interactions between an area of the substrate binding pocket deemed the "back-wall" and the hemiketal ring of the macrolide substrate.