Given our previous results that the DUF575 domain enables cluster proteins to bind to specific membranes during ectopic expression (Figures 2–5), that Mbp1 and Mbp4 are colocalizing with Momp on adhering EBs (Figure 6), but are unable to block a subsequent chlamydial infection as typical chlamydial adhesins do, we conclude that they could be surface localized membrane binding proteins, which use the DUF575 domain to bind to the outer chlamydial membrane and are integral part of the surface of Cpn EBs. Here, CPN1 is linked to chlamydia trachomatis infectious disease.