1.B.70 The Outer Membrane Channel (OMC) Family
The OMC family consists of putative porins that are homologous to many other porins although this particular family is poorly characterized. These proteins are derived from proteobacteria of the alpha, beta and gamma subphyla as well as chlorobi and planctomycetes and probably other phyla. They are therefore wide spread in Gram-negative bacteria.
Putative outer membrane porin
OMP of Acinetobacter johnsonii (D0SAV4)
Putative porin of 450 aas
Porin of Pelodictyon luteolum
Probable porin of 345 aas and 16 beta strands, RopA1. Required for infection by two phage, ΦM12 and N3 (Crook et al. 2013).
RopA1 of Sinorhizobium meliloti
Putative porin of 506 aas, BLpp. Induced by glyphosate (N-[phosphonomethyl] glycine) when applied to Bradyrhizobium sp. (Lupinus)-nodulated lupin plants but not when applied to free living cultures (de María et al. 2007).
BLpp of Bradyrhizobium sp. (Lupinus)
Outer membrane porin, RopAe of 338 aas. It is induced by copper deficiency and transports copper ions (González-Sánchez et al. 2018).
RopAe of Rhizobium etli
Omp43 of 402 aas and 1 N-terminal TMS. This 43-kDa OMP is the major porin protein in Bartonella henselae strains, and its loss leads to changes to the expression of many genes (Kang et al. 2018).
Omp43 of Bartonella henselae
Porin Omp2B of 362 aas. Allows facilitated diffusion of solutes through the porin (Vassen et al. 2019). Among surface protein antigens, the Omp2a and Omp2b porins display the highest diversity in Brucella species. The genes coding for these proteins are closely linked in the Brucella genome and oriented in opposite directions. They share between 85 and 100% sequence identity depending on the Brucella species, biovar, or genotype. Only the omp2b gene copy has been shown to be expressed, and genetic variation is extensively generated by gene conversion between the two copies. Size reduction occurred affecting the region encoding the surface L5 loop of the porin, previously shown to be critical in sugar permeability, followed by a nucleotide reduction in the surface L8 loop-encoding region. It resulted in a final omp2b gene size shared between two distinct clades of non-classical Brucella spp. (African bullfrog isolates) and the group of classical Brucella species (Leclercq et al. 2019).
Omp2B of Brucella abortus
OmpIIIA or RopA of 340 - 166 aas and 1 N-terminal TMS. RopA and RopB (TC# 1.B.4.2.19), 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). Based on similarity, they form passive diffusion pores that allow small molecular weight hydrophilic materials to cross the outer membrane.
OmpIIIA or RopA of Rhizobium leguminosarum
HMPREF0731_0100 of Roseomonas cervicalis ATCC 49957
MetexDRAFT_5733 of Methylobacterium extorquens DSM 13060
Putative porin of 539 aas
Porin of Rhodopirellula sallentina