1.B.5 The Pseudomonas OprP Porin (POP) Family

Two Pseudomonas outer membrane porin proteins, both functionally characterized, comprise the POP family. These porins are anion-selective and transport either phosphate (OprP) or pyrophosphate (OprO) as their physiological substrate.

This family belongs to the Outer Membrane Pore-forming Protein I (OMPP-I) Superfamily .



Benz, R., C. Egli, and R.E. Hancock. (1993). Anion transport through the phosphate-specific OprP-channel of the Pseudomonas aeruginosa outer membrane: effects of phosphate, di- and tribasic anions and of negatively-charged lipids. Biochim. Biophys. Acta. 1149: 224-230.

Citak, F., I. Ghai, F. Rosenkötter, L. Benier, M. Winterhalter, and R. Wagner. (2018). Probing transport of fosfomycin through substrate specific OprO and OprP from Pseudomonas aeruginosa. Biochem. Biophys. Res. Commun. 495: 1454-1460.

Hancock, R.E., C. Egli, R. Benz, and R.J. Siehnel. (1992). Overexpression in Escherichia coli and functional analysis of a novel PPi-selective porin, oprO, from Pseudomonas aeruginosa. J. Bacteriol. 174: 471-476.

Hancock, R.E.W., R. Siehnel and N. Martin (1990). Outer membrane proteins of Pseudomonas. Mol. Microbiol. 4: 1069-1075.

Jeanteur, D., J.H. Lakey and F. Pattus (1991). The bacterial porin superfamily: sequence alignment and structure prediction. Mol. Microbiol. 5: 2153-2164.

Jeanteur, D., J.H. Lakey and F. Pattus (1994). The porin superfamily: diversity and common features. In: Bacterial Cell Wall. Edited by Ghuysen, J.M., Hakenbeck, R. Elsevier, Amsterdam, pp. 363-380.

Lapierre, J. and J.S. Hub. (2023). Converging PMF Calculations of Antibiotic Permeation across an Outer Membrane Porin with Subkilocalorie per Mole Accuracy. J Chem Inf Model 63: 5319-5330.

Modi, N., I. Bárcena-Uribarri, M. Bains, R. Benz, R.E. Hancock, and U. Kleinekathöfer. (2013). Role of the central arginine R133 toward the ion selectivity of the phosphate specific channel OprP: effects of charge and solvation. Biochemistry 52: 5522-5532.

Modi, N., I. Bárcena-Uribarri, M. Bains, R. Benz, R.E. Hancock, and U. Kleinekathöfer. (2015). Tuning the affinity of anion binding sites in porin channels with negatively charged residues: molecular details for OprP. ACS Chem Biol 10: 441-451.

Modi, N., S. Ganguly, I. Bárcena-Uribarri, R. Benz, B. van den Berg, and U. Kleinekathöfer. (2015). Structure, Dynamics, and Substrate Specificity of the OprO Porin from Pseudomonas aeruginosa. Biophys. J. 109: 1429-1438.

Nikaido, H. (1992). Porins and specific channels of bacterial outer membranes. Mol. Microbiol. 6: 435-442.

Niramitranon, J., M.S. Sansom, and P. Pongprayoon. (2016). Why do the outer membrane proteins OmpF from E. coli and OprP from P. aeruginosa prefer trimer? Simulation studies. J Mol Graph Model 65: 1-7. [Epub: Ahead of Print]

Rehm, B.H., G. Boheim, J. Tommassen, and U.K. Winkler. (1994). Overexpression of algE in Escherichia coli: subcellular localization, purification, and ion channel properties. J. Bacteriol. 176: 5639-5647.

Schulz, G.E. (1996). Porins: general to specific, native to engineered passive pores. Curr. Opin. Struc. Biol. 6: 485-490.

Siehnel, R., N.L. Martin and R.E.W. Hancock (1990). Sequence and relatedness in other bacteria of the Pseudomonas aeruginosa oprP gene coding for the phosphate-specific porin P. Mol. Microbiol. 4: 831-838.


TC#NameOrganismal TypeExample

Outer membrane phosphate-selective porin OprP (PorP) of 440 aas.  Binds and transports a variety of mono, di- and trivalent anions (Benz et al. 1993).  An arginine in the pore determines the anion selectivity (Modi et al. 2013).  Residues involved in anion affinity and a preference for Pi versus P2 have been identified (Modi et al. 2015).  Both monomeric and trimeric OprP are belived to maintain their anion selectivity (Niramitranon et al. 2016). The phosphonic-acid antibiotic fosfomycin is highly permeable through the OprO and OprP channels (Citak et al. 2018).


OprP of Pseudomonas aeruginosa


Putative polyphosphate porin, OprO


OprO of Rhodopirellula baltica


Phosphate-selective porin OmpO/P of 412 aas


OmpO/P of Verrucomicrobiae bacterium


Anion-selective porin O/P


Porin O/P of Salinibacter ruber


Anion-selective porin O/P


Porin O/P of Salinibacter ruber


Porin of 627 aas with an N-terminal domain of about 140 aas that is recognized by CDD as a tumor supressor myostatin domain (Pfam 13868).


Porin fusion protein of Gluconobacter morbifer


Phosphate/pyrophosphate-specific porin of 625 aas, OprP/OprO/OprD.


OprD/O/P of Methylophaga aminisulfidivorans


Pyrophosphate-selective porin OprO (Hancock et al. 1992).  The residue basis for the selectivity of P2 over Pi has been determined and involves two residues (Modi et al. 2015).  The phosphonic-acid antibiotic fosfomycin is highly permeable through the OprO and OprP channels (Citak et al. 2018). Fosfidomycin is also transported (Lapierre and Hub 2023).


OprO of Pseudomonas aeruginosa


Outer membrane porin, OprP


OprP of Rhodopirellula baltica


Outer membrane putative phosphate-specific porin, OprP


OprP of Pseudoalteromonas atlantica


Putative outer membrane porin


OMP of Capnocytophaga ochracea


Putative outer membrane porin


OMP of Bacteroides helcogenes


Putative phosphate-specific porin


OMP of Singulisphaera acidiphila


Putative porin O


Porin O of Coraliomargarita akajimensis


Porin O


Porin O of Shewanella violacea


TC#NameOrganismal TypeExample

Putative porin


Putative porin of Sideroxydans lithotrophicus


Putative porin


Porin of Thermocrinis albus