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).


 

References:

Jain, S., S. Kumar, S. Dohre, P. Afley, N. Sengupta, and S.I. Alam. (2014). Identification of a protective protein from stationary-phase exoproteome of Brucella abortus. Pathog Dis 70: 75-83.
Lopes-Rodrigues, M., D. Zanuy, C. Alemán, C. Michaux, and E.A. Perpète. (2019). 3D structure of a porin: molecular modelling in lipid membranes. J Biomol Struct Dyn 37: 3923-3935.
Marquis, H. and T.A. Ficht. (1993). The omp2 gene locus of Brucella abortus encodes two homologous outer membrane proteins with properties characteristic of bacterial porins. Infect. Immun. 61: 3785-3790.
Mobasheri, H., T.A. Ficht, H. Marquis, E.J. Lea, and J.H. Lakey. (1997). Brucella Omp2a and Omp2b porins: single channel measurements and topology prediction. FEMS Microbiol. Lett. 155: 23-30.
Paquet, J.Y., C. Vinals, J. Wouters, J.J. Letesson, and E. Depiereux. (2000). Topology prediction of Brucella abortus Omp2b and Omp2a porins after critical assessment of transmembrane beta strands prediction by several secondary structure prediction methods. J Biomol Struct Dyn 17: 747-757.
Roussel, G., A. Matagne, X. De Bolle, E.A. Perpète, and C. Michaux. (2012). Purification, refolding and characterization of the trimeric Omp2a outer membrane porin from Brucella melitensis. Protein Expr Purif 83: 198-204.
Examples:

TC#NameOrganismal TypeExample
1.B.64.1.1

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).

Bacteria

Omp2a of Brucella melitensis biovar Abortus

 
1.B.64.1.2

Outer membrane porin of 428 aas, Omp2

Proteobacteria

Omp2 of Rhizobium freirei

 
1.B.64.1.3

Putative porin of 384 aas.

Porin of Agrobacterium deltaense