Forms pores that allow passive diffusion of small molecules across the outer membrane. Homotrimer. Forms mixed heterotrimers with OmpC and with PhoE; other mixed heterotrimers are also probable. Expressed at low osmolarity, not expressed at high osmolarity (at protein level). Expression is under the control of OmpR-EnvZ two-component system; not expressed in the absence of ompR-envZ (at protein elevel). No visible effect on infection of HeLa cells. Belongs to the Gram-negative porin family.