The major outer membrane protein of Chlamydia contains four symmetrically spaced variable domains (VDs I to IV). This protein is believed to be an integral part to the pathogenesis, possibly adhesion. Along with the lipopolysaccharide, the major out membrane protein (MOMP) makes up the surface of the elementary body cell. The MOMP is the protein used to determine the different serotypes.

1: Chlamydia trachomatis-host cell interactions: role of the chlamydial major outer membrane protein as an adhesin. Su H, Watkins NG, Zhang YX, Caldwell HD; Infect Immun 1990;58:1017-1025. PMID:2318528