MOLECULAR CHARACTERIZATION OF A 40-KDA OUTER-MEMBRANE PROTEIN, FOMA, OF FUSOBACTERIUM-PERIODONTICUM AND COMPARISON WITH FUSOBACTERIUM-NUCLEATUM

The 40 kDa-outer membrane protein FomA of Fusobacterium periodonticum ATCC 33693 was found to exhibit heat modifiable properties, typical fo r a porin, and N-terminal sequencing indicated a close relationship to the porin FomA of Fusobacterium nucleatum. A polymerase chain reactio n approach was therefore applied for sequencing the fomA gene of F. pe riodonticum, and nucleotide and deduced amino acid sequences were alig ned and compared with the corresponding sequences of different strains of F. nucleatum. In all strains we found a common protein upstream of the fomA gene. The noncoding area upstream of the putative -35 region of the F. periodonticum fomA gene exhibited little sequence similarit y with the F. nucleatum gene. The transcriptional unit of FomA, on the other hand, was very similar, with the similarities concentrated in d omains that were interspersed with hypervariable regions. A topology m odel was made and compared with those made for F. nucleatum. This indi cated that the great similarities reside in the membrane-spanning segm ents of the protein, while most cell surface exposed loops were hyperv ariable. The results strongly support the proposed model for FomA and also indicate that these taxa are related but on a lower level than th e subspecies level. The codon usage of F. periodonticum is comparable to that of F. nucleatum, and the triplet AGA is the only codon used fo r arginine.