Acylation of the 47-kilodalton Major Membrane Immunogen of Treponema Pallidum Determines Its Hydrophobicity

The 47-kilodalton (kDa) major integral membrane immunogen of Treponema pallidum was recently found to be a proteolipid. Similar two-dimensional electrophoretic mobilities and common hydrophobic properties displayed by the native (T. pallidum) and recombinant (Escherichia coli) 47-kDa antigens suggested that the recombinant antigen also possesses covalently bound lipid. Both intact E. coli and E. coli minicells acylated the 47-kDa antigen; immunoprecipitation with a monoclonal antibody specific for the 47-kDa immunogen supported the contention that the acylated product of E. coli corresponds to the cloned T. pallidum antigen. Triton X-114 phase partitioning was used to compare the relative hydrophobicities of 47-kDa molecules synthesized by in vitro and in vivo protein translation systems. The products synthesized by T. pallidum, intact E. coli, or E. coli minicells were hydrophobic, while the protein synthesized in an E. coli cell-free translation system was hydrophilic. Processing experiments with E. coli suggested that the primary gene translation product of the protein is not synthesized in a precursor form, unlike other bacterial proteolipids. These results indicate that the hydrophobicity of the 47-kDa integral membrane protein is conferred substantially by the covalently attached lipid(s). The biochemical similarities between the native and recombinant 47-kDa proteolipids will provide a foundation for future investigations into the structure and immunogenicity of this integral membrane protein of T. pallidum.