1.B.64 The Brucella Omp2 Porin (B-Omp2) Family
In Brucella abortus, a gene encoding a major cell envelope protein, omp2, is duplicated within a short segment of the large chromosomal DNA (Marquis and Ficht 1993). The genes, omp2a or omp2b, were expressed in Escherichia coli. Both gene products localized to the outer membrane. Initial rates of transport of [14C]maltose and growth rates in the presence of maltodextrins of defined size indicated an increased hydrophilic permeability of transformants expressing omp2a. These cells grow on maltotetraose, molecular mass of 667 Da. Activity consistent with the formation of pores has been demonstrated in transformants expressing both genes, but Omp2a forms trimers while Omp2b forms monomers (Mobasheri et al. 1997; Roussel et al. 2012; Jain et al. 2014) . A 16 stranded beta barrel porin has been proposed (Paquet et al. 2000).
The generaiized reaction demonstrated for Brucella Omp2a is:
Sugars (out) → Sugars (in).
Omp2a porin of 386 aas. The 3-d structure reveals a 16-stranded β-barrel with an α-helix on the third loop folding inside the barrel and forming the constriction zone of the channel, a typical feature of general porins (Lopes-Rodrigues et al. 2019). The preferential diffusion of cations over anions has been experimentally observed. Transports maltotetraose (Lopes-Rodrigues et al. 2019).
Omp2a of Brucella melitensis biovar Abortus
Outer membrane porin of 428 aas, Omp2
Omp2 of Rhizobium freirei
Putative porin of 384 aas.
Porin of Agrobacterium deltaense