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1.B.25 The Outermembrane Porin (Opr) Family

The Opr family includes a number of porins in Pseudomonas species and other Gram-negative bacteria that appear to exhibit a variety of substrate selectivities. Thus, OprD2 of P. aeruginosa is specific for cationic amino acids, peptides and antibiotics, while PhaK is specific for phenolic compounds. GusC of E. coli is a 'membrane accessory protein' that facilitates uptake of glucuronides via the GusB permease. Many other specificities have recently been assigned (Tamber et al., 2006).

Tamber et al. (2006) have characterized several of the 19 paralogues in Pseudomonas aeruginosa. They fall into two fairly closely related phylogenetic clusters. Members of one, including OprD, exhibit specificities for amino acids and their derivatives while the other, including PhaK, are specific for organic acids. The six functionally characterized porins determined by Tamber et al. (2006) are provided in the table of the Opr family homologues.

In P. aeruginosa, the majority of small molecules are taken up by members of the OprD outer membrane protein family. Eren et al. (2012) showed that OprD channels require a carboxyl group in the substrate for efficient transport. They have renamed the family Occ, for outer membrane carboxylate channels. Occ channels can be divided into two subfamilies, based on their very different substrate specificities.

Liu et al. (2012) reported that the OccK proteins exhibit fairly distinct unitary conductance values including low (~40-100 pS) and medium (~100-380 pS) conductances. These proteins showed diverse single-channel dynamics of current gating transitions, revealing one (OccK3)-, two (OccK4, OccK5 and OccK6)- and three (OccK1, OccK2 and OccK7)-open sub-state kinetics with functionally distinct conformations. Anion selectivity is a conserved trait among the members of the OccK subfamily, confirming the presence of a net pool of positively charged residues within their central constriction.

The generalized transport reaction catalyzed by members of the Opr family is:

substrate (out) substrate (periplasm)

 

This family belongs to the: Porin Superfamily I.

References associated with 1.B.25 family:

Biswas, S., M.M. Mohammad, L. Movileanu, and B. van den Berg. (2008). Crystal structure of the outer membrane protein OpdK from Pseudomonas aeruginosa. Structure 16: 1027-1035. 18611376
Clark, T.J., C. Momany, and E.L. Neidle. (2002). The benPK operon, proposed to play a role in transport, is part of a regulon for benzoate catabolism in Acinetobacter sp. strain ADP1. Microbiology 148: 1213-1223. 11932465
Eren, E., J. Vijayaraghavan, J. Liu, B.R. Cheneke, D.S. Touw, B.W. Lepore, M. Indic, L. Movileanu, and B. van den Berg. (2012). Substrate specificity within a family of outer membrane carboxylate channels. PLoS Biol 10: e1001242. 22272184
Liang, W.-J., K.J. Wilson, H. Xie, J. Knol, S. Suzuki, N.G. Rutherford, P.J.F. Henderson, and R.A. Jefferson. (2005). The gusBC genes of Escherichia coli encode a glucuronide transport system. J. Bacteriol. 187: 2377-2385. 15774881
Liu, J., E. Eren, J. Vijayaraghavan, B.R. Cheneke, M. Indic, B. van den Berg, and L. Movileanu. (2012). OccK channels from Pseudomonas aeruginosa exhibit diverse single-channel electrical signatures but conserved anion selectivity. Biochemistry 51: 2319-2330. 22369314
Ochs, M.M., C.-D. Lu, R.E.W. Hancock, and A.T. Abdelal. (1999). Amino acid-mediated induction of the basic amino acid-specific outer membrane porin OprD from Pseudomonas aeruginosa. J. Bacteriol. 181:5426-5432. 10464217
Olivera, E.R., B. Miñambres, B. Garcìa, M.A. Moreno, A, Ferràndez, E. Dìaz, J.L. Garcìa, and J.M. Luengo. (1998). Molecular characterization of the phenylacetic acid catabolic pathway in Pseudomonas putida U: the phenylacetyl-CoA catabolon. Proc. Natl. Acad. Sci. USA 95: 6419-6424. 9600981
Rivera, S.L., E. Vargas, M.I. Ramírez-Díaz, J. Campos-García, and C. Cervantes. (2008). Genes related to chromate resistance by Pseudomonas aeruginosa PAO1. Antonie Van Leeuwenhoek 94: 299-305. 18446454
Tamber, S., E. Maier, R. Benz, and R.E. Hancock. (2007). Characterization of OpdH, a Pseudomonas aeruginosa porin involved in the uptake of tricarboxylates. J. Bacteriol. 189: 929-939. 17114261
Tamber, S., M.M. Ochs, and R.E. Hancock. (2006). Role of the novel OprD family of porins in nutrient uptake in Pseudomonas aeruginosa. J. Bacteriol. 188: 45-54. 16352820
Trias J. and H. Nikaido. (1990). Protein D2 channel of the Pseudomonas aeruginosa outer membrane has a binding site for basic amino acids and peptides. J. Biol. Chem. 265: 15680-15684. 2118530
Wang, Y., X. Zhao, B. Sun, H. Yu, and X. Huang. (2012). Molecular dynamics simulation study of the vanillate transport channel of Opdk. Arch Biochem Biophys 524: 132-139. 22633976