Antigenic interrelationship between endoflagella of Treponema phagedenis biotype Reiter and Treponema pallidum (Nichols): molecular characterization of endoflagellar proteins.

Purified endoflagella from nonpathogenic Treponema phagedenis biotype Reiter were characterized biochemically and compared antigenically with the endoflagellar proteins of Treponema pallidum. T. phagedenis biotype Reiter endoflagella were dissociated into constituent polypeptides by incubation under conditions which disrupt noncovalent bonds. Chymotrypsin peptide maps of T. phagedenis biotype Reiter endoflagellar proteins revealed that the 37- and 33-kilodalton (kDa) major components shared significant homology with the 27- and 30-kDa minor components, respectively. The peptide maps also suggested that the major components shared a lesser degree of structural similarity with each other. These relationships were confirmed by Western blots of T. phagedenis biotype Reiter endoflagellar proteins employing antibodies that were purified against the individual endoflagellar polypeptides. Western blots of T. pallidum with the purified antibodies also demonstrated strong cross-reactivity between the T. phagedenis biotype Reiter endoflagellar proteins and T. pallidum proteins of identical or similar molecular weights. A unique Western blotting technique that we called epitope bridging was used to determine that the 37-kDa subunit contains most of the external epitopes on T. phagedenis biotype Reiter endoflagella. Immunoelectron microscopy with human syphilitic serum and rabbit T. phagedenis biotype Reiter endoflagellar antiserum confirmed the presence of cross-reactive epitopes on the surface of intact T. phagedenis and T. pallidum endoflagella.