INTERACTION OF OUTER ENVELOPE PROTEINS OF CHLAMYDIA-PSITTACI GPIC WITH THE HELA-CELL SURFACE

The chlamydial life cycle involves the intimate interaction of compone nts of the infectious elementary body (EB) surface with receptors on t he susceptible eukaryotic cell plasma membrane. We have developed an i n vitro ligand binding assay system for the identification acid charac terization of detergent-extracted EB envelope proteins capable of bind ing to glutaraldehyde-fixed HeLa cell surfaces. With this assay, the d evelopmentally regulated cysteine-rich envelope protein Omp2 of Chlamy dia psittaci strain guinea pig inclusion conjunctivitis was shown to b ind specifically to HeLa cells. HeLa cells bound Omp2 selectively over other cell wall-associated proteins, including the major outer membra ne protein, and the binding of Omp2 was abolished under conditions whi ch alter its conformation. Furthermore, trypsin treatment, which reduc es EB adherence, resulted in the proteolytic removal of a small termin al peptide of Omp2 at the EB surface and inactivated Omp2 in the ligan d binding assay, while having a negligible effect on the major outer m embrane protein, Collectively, our results suggest that Omp2 possesses the capacity to engage in a specific interaction with the host eukary otic cell. We speculate that, since Omp2 is present only in the infect ious EB form, the observed in vitro interaction may be representative of a determining step of the chlamydial pathogenic process.