One route by which Chlamydia trachomatis is internalized into host endometrial epithelial cells is receptor-mediated endocytosis. Although this implies an adhesin-receptor interaction exists, specific chlamydial surface molecules have not been identified. We are investigating potential adhesin molecules using an in vitro functional assay to select for chlamydial recombinant Escherichia coli expressing an adherent phenotype. We have previously shown that E. coli JM109(pPBW58) attaches to epithelial cells by a specific process paralleling C. trachomatis and expresses at least three plasmid-encoded
proteins (18, 28, and 82 kDa; Schmiel, D. H., Knight, S. T., Raulston, J. E., Choong, J., Davis, C. H., and Wyrick, P. B. (1991) Infect. Immun. 59, 4001-4012). In this report, we demonstrate that (i) the 82-kDa
protein is associated with the outer membrane of both E. coli JM109-(pPBW58) and C. trachomatis serovar E elementary bodies; (ii) the plasmid-encoded
protein is identical to the native chlamydial
protein by mass, charge, antigenicity, and partial proteolytic
peptide profiles; (iii) a highly homologous
protein is present in C. trachomatis biovariant
lymphogranuloma venereum; (iv) the 82-kDa
protein is not covalently linked by
disulfide bonds to other
protein species in either E. coli JM109(pPBW58) or C. trachomatis; (v) sequence analysis of the open reading frame indicates this
protein is a relative of the heat shock 70 family of
proteins; and (vi) the inferred amino acid sequence contains a contiguous 73-amino
acid region having 51% identity with the extracellular
sperm receptor binding domain in Strongylocentrosus purpuratus (Foltz, K. R., Partin, J. S., and Lennarz, W. J. (1993) Science 259, 1421-1425). The potential involvement of an hsp70
protein in attachment may provide new insight on adherence mechanisms by obligate intracellular pathogens.