In elementary bodies (EBs, the infectious stage, which is able to survive outside the host cell) provides the structural integrity of the outer envelope through disulfide cross-links with the small cysteine-rich protein and the large cysteine-rich periplasmic protein. It has been described in publications as the Sarkosyl-insoluble COMC (Chlamydia outer membrane complex), and serves as the functional equivalent of peptidoglycan (By similarity). Permits diffusion of specific solutes through the outer membrane. Part of a disulfide cross-linked outer membrane complex (COMC) composed of the major outer membrane porin, the small cysteine-rich protein (OmcA) and the large cysteine-rich periplasmic protein (OmcB). It is present but some of the disulfide bonds are reduced in the intracellular reticulate bodies (RBs). Belongs to the chlamydial porin (CP) (TC 1.B.2) family.