Abstact

It has been recently realized that some Gram-negative organisms such as Escherichia coli produce a multiheme cytochrome c to serve as a quinol peroxidase that couples electrons from the quinol pool directly to H2O2. The E. coli version of this enzyme, termed YhjA, has been predicted to be a member of the bacterial cytochrome c peroxidase (bCCP) superfamily, where a novel N-terminal single-heme binding domain is fused to the canonical bCCP diheme domain found widely in Gram-negative bacteria. Here, we present an X-ray crystal structure of YhjA, revealing the triheme architecture that nature has employed to couple the quinol pool to the reduction of H2O2. We also show kinetic, spectroscopic, and electrochemical data that detail the differences between the three hemes that are observed in the structure, where two of the heme irons are both six-coordinate, ligated by Met and His residues, and the third peroxidatic heme is found to be five-coordinate. Electrocatalytic voltammetry of YhjA illustrates how the high-potential hemes serve as relays to the peroxidatic active site. Together, these data suggest a model of the catalytic chemistry of YhjA, illustrating how this member of the bCCP family may react with substrates and engage in multielectron redox reactions.