Crystal structure and biochemical studies of the trans-acting polyketide enoyl reductase LovC from lovastatin biosynthesis

Lovastatin is an important statin prescribed for the treatment and prevention of cardiovascular diseases. Biosynthesis of lovastatin uses an iterative type I polyketide synthase (PKS). LovC is a transacting enoyl reductase (ER) that specifically reduces three out of eight possible polyketide intermediates during lovastatin biosynthesis. Such trans-acting ERs have been reported across a variety of other fungal PKS enzymes as a strategy in nature to diversify polyketides. How LovC achieves such specificity is unknown. The 1.9-angstrom structure of LovC reveals that LovC possesses a medium-chain dehydrogenase/reductase (MDR) fold with a unique monomeric assembly. Two LovC cocrystal structures and enzymological studies help elucidate the molecular basis of LovC specificity, define stereochemistry, and identify active-site residues. Sequence alignment indicates a general applicability to trans-acting ERs of fungal PKSs, as well as their potential application to directing biosynthesis.