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

Abstract

Hydroperoxides are reactive oxygen species (ROS) that are toxic to all cells and must be converted into the corresponding alcohols to alleviate oxidative stress. InEscherichia coli, the enzyme primarily responsible for this reaction is alkylhydroperoxide reductase (AhpR). Here, the crystal structures of both of the subunits ofEcAhpR,EcAhpF (57 kDa) andEcAhpC (21 kDa), have been solved. TheEcAhpF structures (2.0 and 2.65 Å resolution) reveal an open and elongated conformation, while that ofEcAhpC (3.3 Å resolution) forms a decameric ring. Solution X-ray scattering analysis ofEcAhpF unravels the flexibility of its N-terminal domain, and its binding toEcAhpC 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.