This family consists of the general diffusion porins from mainly the Beta and Gamma subdivisions of Proteobacteria. Although the porins of this family share common structural and functional properties with the porins of General Bacterial Porin Family 2 (GBP-2) and the Rhodobacter porin family, their sequence similarity is rather low. The porins form large aqueous channels, facilitating the diffusion of small hydrophilic molecules through the outer membrane in a non-specific manner. Important aspects of the channel activity are the conductance, the voltage dependence and the pH sensitivity. Several porins of this family have been determined at low resolution (Omp32, OmpF, Phosphoporin, OmpK36) suggesting that the 16-stranded ß-barrel is a common structural feature. In addition to that, the porins of this family seem to require trimerization in order to function properly. In Providencia stuartii, these porins form primitive junctions between P. stuartii cells. These junctions could foster the formation of floating communities and support intercellular communications.

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