Molecular cloning and characterization of a 35.5-kilodalton lipoprotein of Treponema pallidum.

A clone expressing a 35.5-kDa recombinant treponemal protein was isolated from a genomic DNA library constructed from Treponema pallidum street strain 14. Polyclonal antiserum raised against the recombinant protein reacted with a corresponding native protein of comparable size in T. pallidum that is specific to the pathogenic treponemes. Radiolabeling of the recombinant protein with [3H]palmitate demonstrated that it is lipid modified. Like other recently characterized T. pallidum lipoproteins, the 35.5-kDa lipoprotein partitioned into the detergent phase from T. pallidum cells fractionated with Triton X-114, suggesting that it is an integral membrane protein. Processing of the recombinant 35.5-kDa lipoprotein from a precursor form to a smaller mature form was not evident in pulse-chase experiments. However, pretreatment of Escherichia coli cells expressing the 35.5-kDa lipoprotein with inhibitors of protein processing or translocation revealed the existence of a higher-molecular-mass precursor. Gene fusion studies with the transposon TnphoA demonstrated the presence of an export signal in the 35.5-kDa lipoprotein that promotes the extracytoplasmic localization of a 35.5-kDa lipoprotein-PhoA hybrid.