1.B.19 The Glucose-selective OprB Porin (OprB) Family
The OprB family of outer membrane porins includes proteins from α-, β-, γ- and δ-proteobacteria including species of Pseudomonas, Acinetobacter, Xanthomonas, Ralstonia, Bradyrhizobium, and other organisms including cyanobacteria, flavobacteria, planctomyces and chlamydia. Some of the Pseudomonas homologues have been reconstituted in proteoliposomes and characterized (Adewoye et al., 1998). The Km for glucose of the P. aeruginosa homologue is 4 μM. It exhibits high specificity for glucose, but also transports glycerol, mannitol and fructose (Wylie and Worobec, 1993). They have 40-50% β-structure. The oprB gene is adjacent to the gltK gene encoding an ATPase of a probable glucose ABC transporter. oprB expression is induced by glycerol and glucose limitation, repressed by salicylate, and responsive to temperature and pH (Adewoye and Worobec, 1999).
A second member of the family is OprB of Burkholderia pseudomallei (TC #1.B.19.1.2; Chan et al., 2007). This functions in conjunction with BpeAB (TC #2.A.6.2.23) to export several quorum sensing acyl homoserine lactones with acyl chains of 8-14 carbons.