PscC

PscC is a diheme cytochrome c subunit of the photosynthetic reaction center found in certain purple bacteria, including Rhodobacter and Rhodopseudomonas species. It is encoded by the pscC gene as part of the photosynthesis gene cluster that also contains other RC components such as pscA, pscB, and pscD. PscC is a relatively small, periplasmic protein that carries two heme cofactors, a hallmark of c-type cytochromes, enabling it to participate in electron transfer processes associated with the reaction center.

Structure and localization: PscC binds two hemes via covalent attachments typical of c-type cytochromes and is positioned on the periplasmic side of the photosynthetic RC. The arrangement of the two hemes supports sequential electron transfer, acting as a conduit between upstream electron carriers and the reaction center core.

Function and mechanism: The protein functions as an electron transfer mediator, delivering electrons to the reaction center to replenish the donor side after light-driven charge separation. It interacts with RC components, including core subunits such as PscA, and with auxiliary cytochromes. The exact electron transfer pathway can vary among species and environmental conditions, but PscC generally facilitates efficient electron flow from soluble periplasmic cytochromes to the reaction center.

Genetics and evolution: PscC is part of the conserved psc gene cluster found in many purple photosynthetic bacteria, with expression typically linked to photosynthetic growth under anaerobic conditions. Comparative studies have highlighted its relationship to other multicofactor cytochromes involved in bacterial photosynthesis.

Research context: PscC has been characterized through biochemical and structural studies in diverse purple bacteria, contributing to understanding of the periplasmic electron transfer network that supports bacterial photosynthesis.