Overexpression and surface localization of the Chlamydia trachomatis major outer membrane protein in Escherichia coli.

The Chlamydia trachomatis major outer membrane protein (MOMP) is the quantitatively predominant surface protein which has important functional, structural and antigenic properties. We have cloned and overexpressed the MOMP in Escherichia coli. The MOMP is surface exposed in C. trachomatis and capable of eliciting protective antibodies in infected hosts, and therefore has potential as a candidate vaccine to prevent infection with this significant human pathogen. The recombinant MOMP clone, L2rMOMP, contained the entire MOMP gene including the encoded leader sequence. Large quantities of chlamydial MOMP were expressed, some of which was processed and translocated to the E. coli surface. Surface localization of the MOMP was demonstrated by the binding of anti-MOMP monoclonal antibodies to the surface of the induced clone, and was visualized by fluorescence and electron microscopy. The induction of MOMP expression had a rapidly lethal effect on the L2rMOMP E. coli clone. Although no genetic system exists for Chlamydia, development of a stable, inducible E. coli clone which overexpresses the chlamydial MOMP permits a study of the biological properties of the MOMP, including the contribution of the MOMP variable segments to the topographical interactions which determine the antigenic structure responsible for human immune response.