This family represents a conserved region approximately 400 residues long within the bacterial phosphate-selective porins O and P. These are anion-specific porins, the binding site of which has a higher affinity for phosphate than chloride ions. Porin O has a higher affinity for polyphosphates, while porin P has a higher affinity for orthophosphate [1]. In P. aeruginosa, porin O was found to be expressed only under phosphate-starvation conditions during the stationary growth phase [2].

1: Overexpression in Escherichia coli and functional analysis of a novel PPi-selective porin, oprO, from Pseudomonas aeruginosa. Hancock RE, Egli C, Benz R, Siehnel RJ; J Bacteriol 1992;174:471-476. PMID:1370289

2: Polyphosphate-selective porin OprO of Pseudomonas aeruginosa: expression, purification and sequence. Siehnel RJ, Egli C, Hancock RE; Mol Microbiol 1992;6:2319-2326. PMID:1406271