1.B.4 The Brucella-Rhizobium Porin (BRP) Family

The porin proteins in the BRP family are found in the Agrobacterium, Bartonella, Brucella, Mesorhizobium and Rhizobium genuses and are likely to be found in other closely related genera. Brucella species have two homologous outer membrane porins, Omp2a and Omp2b, encoded by two closely linked genes oriented in oppostie directions. Omp2 proteins exist in many size variants due to multiple gene conversions between the two homologous genes that lead to chimeric proteins. These variants show different permeability to sugars as well as different ion conductivities (Paquet et al. 2001). This family is also called the Omp2 family in SwissProt.

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



Cloeckaert, A., H.S. Debbarh, N. Vizcaino, E. Saman, G. Dubray, and M.S. Zygmunt. (1996). Cloning, nucleotide sequence, and expression of the Brucella melitensis bp26 gene coding for a protein immunogenic in infected sheep. FEMS Microbiol. Lett. 140: 139-144.

Cloeckaert, A., J.M. Verger, M. Grayon, and N. Vizcaino. (1996). Molecular and immunological characterization of the major outer membrane proteins of Brucella. FEMS Microbiol Lett. 145: 1-8.

Hohle, T.H., W.L. Franck, G. Stacey, and M.R. O'Brian. (2011). Bacterial outer membrane channel for divalent metal ion acquisition. Proc. Natl. Acad. Sci. USA 108: 15390-15395.

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.

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

Paquet, J.Y., M.A. Diaz, S. Genevrois, M. Grayon, J.M. Verger, X. de Bolle, J.H. Lakey, J.J. Letesson, and A. Cloeckaert. (2001). Molecular, antigenic, and functional analyses of Omp2b porin size variants of Brucella spp. J. Bacteriol. 183: 4839-4847.

Paul, S., B.V. Peddayelachagiri, S. Nagaraj, J.J. Kingston, and H.V. Batra. (2018). Recombinant outer membrane protein 25c from Brucella abortus induces Th1 and Th2 mediated protection against Brucella abortus infection in mouse model. Mol Immunol 99: 9-18.

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

Vizcaino, N., A. Cloeckaert, M.S. Zygmunt, and G. Dubray. (1996). Cloning, nucleotide sequence, and expression of the Brucella melitensis omp31 gene coding for an immunogenic major outer membrane protein. Infect Immun. 64: 3744-3751.


TC#NameOrganismal TypeExample

Fusion porin protein of 1115 aas with two domains that are homologous to members of family 1.B.4 at the N- and C-termini of this protein and a central domain homologous to members of family 1.B.13 proteins. These fusion proteins are found in several closely related species of α-proteobacteria such as those in the genuses, Methylosinus and Methylocystis (BL Reddy and MH Saier, unpublished observations).


Fusion porin protein of Methylosinus trichosporium


Fusion porin protein of 840 aas with an N-terminal domain that is homologous to members of family 1.B.13, and a C-terminal domain that is homologous to members of family 1.B.4 proteins.  It is 60% identical to the last two domains in 1.B.4.2.15 but it lacks the N-terminal domain of that protein.


Fusion protein of Methylosinus trichosporium


TC#NameOrganismal TypeExample

Hypothetical protein of 259 aas


HP of Coxiella burnetii


Putative porin of 200 aas


PP of Octadecabacter antarcticus


Putative porin of 233 aas


PP of Azorhizobium caulinodans


Porin of 240 aas


Porin of Brucella canis


Putative porin of 199 aas


PP of Octadecabacter antarcticus

1.B.4.2.15Outer membrane immunogenic protein, Omp31BacteriaOmp31 of Brucella melitensis (Q45322)

High affinity Mn2+ (but not Co2+ or Cu2+) porin, MnoP (675 aas) (Hohle et al., 2011).  This protein seems to be a fusion protein between an Omp_b-br1 family porin (N-terminus) and an OprB porin (C-terminus).  It shows little sequence similiarity with the OprB family proteins of 1.B.19.


MnoP of Bradyrhizobium japonicum (Q89Y60)


Opacity protein of 188 aas


Opacity protein of Sphingomonas witichii


Outer membrane porin, Omp25c, of 228 aas. The collective Th1 plus Th2 immune responses induced by Omp25c protects against Brucella infections (Paul et al. 2018).

Omp25c of Brucella abortus



Uncharacterized porin homologue of 242 aas.  Shows similarity with 9.B.184.1.1 which also shows similarity with members of 1.B.6; it is likely to be a porin.


Putative porin of Bradyrhizobium sp. ORS 285


Putative porin


Putative porin of Rhizobium sp. AP16


Putative porin


Putative porin of Bradyrhizobium japonicum


Putative porin of 252 aas


Porin of Bradyrhizobium sp.


Porin of 252 aas


Porin of Xanthobacter autotrophicus


Putative porin of 289 aas


Putative porin of Methylobacterium extorquens


Porin of 241 aas


Porin of Nitrobacter winogradskyi


Probable carbohydrate-selective outer membrane porin, OprB, of 302 aas (Brunen et al. 1991).


OMP of Acidovorax delafiedii


TC#NameOrganismal TypeExample