AhpC

ahpC encodes alkyl hydroperoxide reductase subunit C, a bacterial peroxiredoxin involved in the oxidative stress response. The protein is part of the peroxide-detoxifying machinery that helps cells neutralize hydroperoxides, including hydrogen peroxide and organic peroxides, thereby protecting cellular components from oxidative damage. In many bacteria, ahpC is expressed under stress conditions and contributes to the overall peroxide resistance of the cell.

Functionally, AhpC reduces peroxides to their corresponding alcohols or water. Electron donation typically comes from a partner protein, such as AhpF in the common AhpCF system, which regenerates AhpC after peroxide reduction. In some species there is an alternative redox arrangement, with AhpD influencing the activity of AhpC. This redundancy allows bacteria to adapt peroxide detoxification to different environmental niches and redox states.

Structurally, AhpC is a small cytosolic enzyme that belongs to the peroxiredoxin family. It contains conserved catalytic cysteine residues that form a catalytic disulfide during turnover. The catalytic cycle begins with oxidation of the peroxidatic cysteine by the peroxide substrate, followed by resolution involving a second cysteine, and subsequent reduction by the partner reductase to reset the enzyme for another cycle.

Regulation and ecological relevance vary by species. ahpC expression is commonly controlled by oxidative stress regulators such as OxyR in many bacteria, enabling rapid upregulation in response to peroxide exposure. In pathogenic microbes, AhpC contributes to survival in the host’s oxidative defenses and can be linked to virulence in some contexts. Across bacteria and archaea, ahpC is widely distributed, often forming part of operons with related redox genes and reflecting a conserved role in peroxide detoxification.