PhoEs

PhoEs is a term used in microbiology to refer to a family of phosphate-starvation–inducible outer membrane porins, most notably the PhoE porin from Escherichia coli. PhoE proteins form channels in the outer membrane that permit passive diffusion of small hydrophilic molecules, including inorganic phosphate, thereby supporting phosphate uptake when external levels are limited. PhoE porins are trimeric in the outer membrane, with each monomer creating a pore that contributes to overall membrane permeability.

Genetically, phoE is part of the Pho regulon. Under phosphate-replete conditions its expression is low, but during phosphate starvation the PhoR/PhoB two-component system becomes activated. Phosphorylated PhoB induces transcription of phoE alongside other phosphate-scavenging genes. The Pho regulon activity is modulated by the PstSCAB transporter and PhoU, providing feedback control to prevent excessive pore expression.

Distribution and function: While best characterized in E. coli, PhoE orthologs are found in related enteric bacteria. The PhoE porin contributes to outer membrane permeability and can influence the uptake of other small solutes; alterations in PhoE expression can affect susceptibility to certain antibiotics that cross the outer membrane via porins.

In research and context, PhoEs are studied as part of porin biology, outer membrane permeability, and nutrient acquisition strategies in Gram-negative bacteria. See also porin, OmpF, OmpC, and the Pho regulon.