*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 I (OMPP-I) Superfamily .
References:
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.
Examples:
TC#	Name	Organismal Type	Example
1.B.4.1.1	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).	Proteobacteria	Fusion porin protein of Methylosinus trichosporium

1.B.4.1.2	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.	Proteobacteria	Fusion protein of Methylosinus trichosporium

Examples:
TC#	Name	Organismal Type	Example
1.B.4.2.10	Hypothetical protein of 259 aas	Proteobacteria	HP of Coxiella burnetii

1.B.4.2.11	Putative porin of 200 aas	Proteobacteria	PP of Octadecabacter antarcticus

1.B.4.2.12	Putative porin of 233 aas	Proteobacteria	PP of Azorhizobium caulinodans

1.B.4.2.13	Porin of 240 aas	Proteobacteria	Porin of Brucella canis

1.B.4.2.14	Putative porin of 199 aas	Proteobacteria	PP of Octadecabacter antarcticus

1.B.4.2.15	Outer membrane immunogenic protein, Omp31	Bacteria	*Omp31 of Brucella melitensis* (Q45322)**

1.B.4.2.16	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.	Bacteria	*MnoP of Bradyrhizobium japonicum* (Q89Y60)**

1.B.4.2.17	Opacity protein of 188 aas	Proteobacteria	Opacity protein of Sphingomonas witichii

1.B.4.2.18	*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

1.B.4.2.19	RopB of 211 aas and 1 N-terminal TMS. RopA (TC# 1.B.70.1.2) and RopB, which have β-barrel structures, may be involved in the control of plant-microbial symbiosis. Kosolapova et al. 2019 demonstrated that the full-length RopA and RopB proteins form amyloid fibrils in vitro. These fibrils are β-sheet-rich, bind Thioflavin T (ThT), exhibit green birefringence upon staining with Congo Red (CR), and resist treatment with ionic detergents and proteases. Heterologously expressed RopA and RopB intracellularly aggregate in yeast and assemble into amyloid fibrils at the surface of E. coli. The capsules of the R. leguminosarum cells bind CR, exhibit green birefringence, and contain fibrils of RopA and RopB in vivo (Kosolapova et al. 2019).		RopB of Rhizobium leguminosarum

1.B.4.2.2	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.	Proteobacteria	*Putative porin of Bradyrhizobium* sp. ORS 285**

1.B.4.2.20	*Omp25 porin of 213 aas. Omp25, LPS and peptidoglycan are incorporated at the new pole and the division site, the expected growth sites (Vassen et al.* 2019).**		*Omp25 of Brucella abortus* biovar 1**

1.B.4.2.3	Putative porin	α-Proteobacteria	*Putative porin of Rhizobium* sp. AP16**

1.B.4.2.4	Putative porin	α-Proteobacteria	Putative porin of Bradyrhizobium japonicum

1.B.4.2.5	Putative porin of 252 aas	Proteobacteria	*Porin of Bradyrhizobium* sp.**

1.B.4.2.6	Porin of 252 aas	Proteobacteria	Porin of Xanthobacter autotrophicus

1.B.4.2.7	Putative porin of 289 aas	Proteobacteria	Putative porin of Methylobacterium extorquens

1.B.4.2.8	Porin of 241 aas	Proteobacteria	Porin of Nitrobacter winogradskyi

1.B.4.2.9	*Probable carbohydrate-selective outer membrane porin, OprB, of 302 aas (Brunen et al.* 1991).**	Proteobacteria	OMP of Acidovorax delafiedii

Examples:
TC#	Name	Organismal Type	Example