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. It is present but some of the disulfide bonds are reduced in reticulate bodies (RBs). 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 (MOMP), the small cysteine-rich protein (OmcA) and the large cysteine-rich periplasmic protein (OmcB). Belongs to the chlamydial porin (CP) (TC 1.B.2) family.