Activity of One of Two Engineered Heterodimers of AhpF, the NADH:Peroxiredoxin Oxidoreductase from Salmonella typhimurium, Reveals Intrasubunit Electron Transfer between Domains

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Abstract
AhpF, the flavoprotein reductase component of the Salmonella typhimurium alkyl hydroperoxide reductase system, catalyzes the reduction of an intersubunit disulfide bond in the peroxidatic active site of the system's other component, AhpC, a member of the peroxiredoxin family. Previous studies have shown that AhpF can be dissected into two functional units, a thioredoxin reductase-like C-terminus (containing FAD and a redox-active disulfide, Cys345−Cys348) and an N-terminal domain containing a second redox-active disulfide center (Cys129−Cys132). The role of the N-terminal domain as the direct reductant of AhpC, mediating electron transfer from the C-terminal redox centers of AhpF, has been firmly established by several approaches. Not known, however, was whether the transfer of electrons between the C-terminal and N-terminal disulfide centers occurred as an inter- or intrasubunit process in dimeric AhpF. Two heterodimeric AhpF species were therefore created in which one of the two pathways was completely disrupted while the other was left partially intact in each construct. Only the heterodimer containing one monomer of wild type AhpF and a monomer of mutated (and truncated) AhpF exhibited peroxidase activity with AhpC indicating that electron transfer between domains of AhpF is an intrasubunit process.