Homology between Borrelia burgdorferi OspC and members of the family of Borrelia hermsii variable major proteins.

Synthesis of the Borrelia burgdorferi outer surface protein C (OspC) is quite variable. We have cloned and sequenced the ospC gene from B. burgdorferi isolate CA-11.2A, a clone in which ospC expression varies. The 5' flanking region of the gene contains at least two consensus promoter regions, as well as two large overlapping inverted repeats. Sequence comparison to other OspC proteins indicated that the CA-11.2A OspC is as closely related to OspC from two different genospecies of Lyme disease spirochetes as it is to OspC from the prototype B. burgdorferi strain, B31. Comparisons of the OspC amino acid (aa) sequence with those in aa sequence databases revealed partial identity with the variable major proteins Vmp3 and Vmp24 of B. hermsii, a causative agent of tick-borne relapsing fever. An ospC probe hybridized to B. hermsii restriction fragments and linear plasmids that also were recognized by the vmp3 and vmp24 probes. OspC and these Vmp appear to be related, but their synthesis is regulated differently in the two species of spirochetes. This represents a fascinating example of the evolution of the number, position, regulation and perhaps function of homologous genes in two related pathogens. These parameters may relate to characteristic properties of the pathogens and their separate tick vectors.