This is a new project which focuses on the expression of the Chlamydia trachomatis major outer membrane protein (MOMP) in Escherichia coli. Evidence suggest that the MOMP serves as an adhesin and that protective immune responses are directed towards MOMP. The expression of MOMP in a system which is amenable to genetic manipulation would provide a useful tool for further studies of MOMP structure and function. Therefore, one of the goals of this project is to express MOMP in E. coli and to use site directed mutagenesis to study the contribution of specific amino acid sequences to structural, functional and antigenic properties. PCR amplification of MOMP sequences has been used to create several plasmids that express MOMP in E. coli cells. MOMP sequences have been fused to the signal peptide and amino terminal end of the E. coli OmpA protein. A second goal of this project is the use of E. coli for expression of MOMP B- and T-cell epitopes as fusions proteins with the B subunit of the E. coli heat-labile toxin (LT). Synthetic peptides which contain MOMP T-cell and B-cell epitopes in tandem have been shown to induce an anamnestic antibody response to the desired B-cell epitope (Su and Caldwell). The E. coli LT B subunit has a specific affinity for the GM1 ganglioside present on mucosal surfaces and has the unusual property of being a potent oral immunogen; thus, the expression of chlamydial epitopes as fusions proteins will facilitate targeting of the epitopes for stimulation of mucosal immunity. Construction and initial characterization of these fusions will be accomplished in the upcoming year.