PstC

PstC is a membrane protein component of the phosphate-specific transport (Pst) ABC transporter found in many bacteria and some archaea. It is encoded together with pstS, pstA and pstB (and often phoU) in the pstSCAB operon. The Pst system mediates high-affinity uptake of inorganic phosphate (Pi) when environmental concentrations are low.

Functionally, PstC pairs with PstA to form the transmembrane permease through which phosphate is translocated. PstS, a periplasmic binding protein, delivers Pi to the PstA–PstC channel, and PstB provides ATP hydrolysis to drive transport. As a polytopic integral membrane protein, PstC typically contains multiple transmembrane helices and contributes to substrate specificity and conformational changes during the transport cycle.

Expression of pst genes is regulated by the Pho regulon, a two-component system (PhoR–PhoB) that responds to phosphate availability. In addition to nutrient uptake, the Pst system influences regulatory networks: loss-of-function mutations in pst components can constitutively activate Pho regulon-controlled genes. Homologs of PstC have been linked to phenotypes such as altered virulence, biofilm formation and stress responses in diverse bacterial pathogens.

PstC is studied using genetic knockouts, biochemical assays, and structural methods applied to ABC transporters, including X-ray crystallography and cryo-electron microscopy of related complexes. Its conservation and regulatory roles make it a subject of interest for understanding phosphate homeostasis and its impact on microbial physiology.