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 large cysteine-rich periplasmic protein and the major outer membrane porin. 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). 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). The protein moiety probably penetrates into the periplasm. It is present but the disulfide bonds are reduced in reticulate bodies (RBs).