Structure, mechanism and ensemble formation of the alkylhydroperoxide reductase subunits AhpC and AhpF fromEscherichia coli

Hydroperoxides are reactive oxygen species (ROS) that are toxic to all cells and must be converted into the corresponding alcohols to alleviate oxidative stress. In Escherichia coli , the enzyme primarily responsible for this reaction is alkylhydroperoxide reductase (AhpR). Here, the crystal structures of both of the subunits of Ec AhpR, Ec AhpF (57 kDa) and Ec AhpC (21 kDa), have been solved. The Ec AhpF structures (2.0 and 2.65 Å resolution) reveal an open and elongated conformation, while that of Ec AhpC (3.3 Å resolution) forms a decameric ring. Solution X-ray scattering analysis of Ec AhpF unravels the flexibility of its N-terminal domain, and its binding to Ec AhpC was demonstrated by isothermal titration calorimetry. These studies suggest a novel overall mechanistic model of AhpR as a hydroperoxide scavenger, in which the dimeric, extended AhpF prefers complex formation with the AhpC ring to accelerate the catalytic activity and thus to increase the chance of rescuing the cell from ROS.