Structural basis of carnitine monooxygenase CntA substrate specificity, inhibition, and intersubunit electron transfer
Mussa Quareshy, Muralidharan Shanmugam, Eleanor R. Townsend, Eleanor Jameson, Timothy D. H. Bugg, Alexander D. Cameron, Yin Chen
Abstract
trimeric structure. The two functional domains (the Rieske and the catalytic mononuclear iron domains) are located >40 Å apart in the same monomer but adjacent in two neighboring monomers. Structural determination of CntA and subsequent electron paramagnetic resonance measurements uncover the molecular basis of the so-called bridging glutamate (E205) residue in intersubunit electron transfer. The structures of the substrate-bound CntA help to define the substrate pocket. Importantly, a tyrosine residue (Y203) is essential for ligand recognition through a π-cation interaction with the quaternary ammonium group. This interaction between an aromatic residue and quaternary amine substrates allows us to delineate a subgroup of Rieske oxygenases (group V) from the prototype ring-hydroxylating Rieske oxygenases involved in bioremediation of aromatic pollutants in the environment. Furthermore, we report the discovery of the first known CntA inhibitors and solve the structure of CntA in complex with the inhibitor, demonstrating the pivotal role of Y203 through a π-π stacking interaction with the inhibitor. Our study provides the structural and molecular basis for future discovery of drugs targeting this TMA-producing enzyme in human gut.