Abstract
MycG is a P450 monooxygenase that catalyzes the sequential hydroxylation and epoxidation of mycinamicin IV (M-IV), the last two steps in the biosynthesis of mycinamicin II, a macrolide antibiotic isolated from Micromonospora griseorubida. The crystal structure of MycG with M-IV bound was previously determined but showed the bound substrate in an orientation that did not rationalize the observed regiochemistry of M-IV hydroxylation. Nuclear magnetic resonance paramagnetic relaxation enhancements provided evidence of an orientation of M-IV in the MycG active site more compatible with the observed chemistry, but substrate-induced changes in the enzyme structure were not characterized. We now describe the use of amide 1H–15N residual dipolar couplings as experimental restraints in solvated “soft annealing” molecular dynamics simulations to generate solution structural ensembles of M-IV-bound MycG. Chemical shift perturbations, hydrogen–deuterium exchange, and 15N relaxation behavior provide insight into the dynamic and electronic perturbations in the MycG structure in response to M-IV binding. The solution and crystallographic structures are compared, and the possibility that the crystallographic orientation of bound M-IV represents an inhibitory mode is discussed.
