A soluble 60 kilo Dalton antigen of Chlamydia spp. is a homologue of Escherichia coli GroEL

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Abstract
Two major 60kD protein species can be separated by differential detergent extraction in Chlamydia spp. A Sarkosyl‐soluble 60kD protein is (i) structurally and antigenically distinct from the previously characterized 60kD Omp2 outer membrane protein; and (ii) antigenically related to a bacterial common antigen of similar molecular weight which includes a 65 kD myco‐bacterial antigen and the GroEL heat‐shook protein of Escherichia coli. Among GroEL homologues, the chlamydial protein (chl‐GroEL) uniquely displays affinity towards immobilized thiol groups. The significance of this property is discussed with respect to the synthesis and assembly of the chlamydial disulphide‐rich cell wall late in the growth cycle. Chl‐GroEL is identical to the Triton X‐100‐soluble, ocular delayed‐type hypersensitivity agent (Morrison et al., 1989), an essential component in the development of blinding trachoma. An autoimmune mechanism for chronic chlamydial diseases based on chl‐GroEL homology to host proteins is hypothesized.