A SURFACE-EXPOSED REGION OF A NOVEL OUTER-MEMBRANE PROTEIN (P66) OF BORRELIA SPP. IS VARIABLE IN SIZE AND SEQUENCE

A model of the 66-kDa outer membrane protein (P66) of Lyme disease Bor relia spp, predicts a surface-exposed loop near the C terminus, This r egion contains an antigen commonly recognized by sera from Lyme diseas e patients, In the present study, this region of P66 and homologous pr oteins of other Borrelia spp, were further investigated by using monoc lonal antibodies, epitope mapping of P66 of Borrelia burgdorferi, and DNA sequencing, A monoclonal antibody specific for B. burgdorferi boun d to the portion of P66 that was accessible to proteolysis in situ, Th e linear epitope for the antibody was mapped within a variable segment of the surface-exposed region, To further study this protein, the com plete gene of Borrelia hermsii for a protein homologous to P66 was clo ned, The deduced protein was 589 amino acids in length and 58% identic al to P66 of B. burgdorferi. The B. hermsii P66 protein was predicted to have a surface-exposed region in the same location as that of B. bu rgdorferi's P66 protein, With primers designed on the basis of conserv ed sequences and PCR, we identified and cloned the same regions of P66 proteins of Borrelia turicatae, Borrelia parkeri, Borrelia coriaceae, and Borrelia anserina, The deduced protein sequences from all species demonstrated two conserved hydrophobic regions flanking a surface-exp osed loop, The loop sequences were highly variable between different B orrelia spp, in both sequence and size, varying between 35 and 45 amin o acids, Although the actual function of P66 of Borrelia spp. is unkno wn, the results suggest that its surface-exposed region is subject to selective pressure.