Objectives: The major outer membrane protein (MompA) of Treponema pectinovorum has been identified and characterized previously. In order to initiate a genetic analysis of its pathogenic role, the gene for MompA was cloned and the protein was expressed in E. coli . Methods: The amino terminal 34 amino acid sequence was determined from the MompA protein. A PCR approach was initiated to generate a portion of the mopA gene and used as the probe to screen libraries of T. pectinovorum genomic DNA. The mature protein-coding region was amplified by a PCR and ligated into pRSETA expression vector and expressed in E. coli. Results: The gene encoding C-terminal portion of the MompA (766 bp) was cloned in E. coli . However, we failed to directly clone the 5'- genomic DNA fragment containing the portion encoding N-terminal of the mature protein, signal peptide, and potential promoter region due to the toxicity of the gene product. This portion of mopA gene sequence was determined by a PCR approach. The nucleotide sequence analysis revealed a 1206-bp open reading frame encoding MompA with a signal peptide. The protein has 402 amino acids with a calculated molecular size of 42.5-kDa. The mature MompA has 382 amino acids with molecular size of 40.5 kDa. Database search of the mopA gene sequence found no significant homology with other published genes from oral treponemes and bacteria. MompA was expressed in E. coli as a 45-kDa fusion protein, which can reacted with anti-MompA antibody in Western blot. Conclusions: The gene encode major outer membrane protein of Treponema pectinovorum was cloned and the protein was expressed which provide a basis for genetic analysis of its pathogenic role of the 42-kDa MompA. Supported by DE-11368 and DE13819.

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