SEQUENCE VARIABILITY OF THE 40-KDA OUTER-MEMBRANE PROTEINS OF FUSOBACTERIUM-NUCLEATUM STRAINS AND A MODEL FOR THE TOPOLOGY OF THE PROTEINS

The complete nucleotide sequences of the fomA genes encoding the 40-kD a outer membrane proteins (OMPs) of strains ATCC 10953 and ATCC 25586 of Fusobacterium nucleatum were determined using the genomic DNA, or D NA fragments ligated into a vector plasmid, as template in a polymeras e chain reaction. The deduced amino acid sequences of these two protei ns were aligned with the amino acid sequence of the corresponding prot ein of F. nucleatum strain Fev1 and examined for conserved/variable po lypeptide segments. A model for the topology of the 40-kDa OMPs is pro posed on the basis of this alignment and application of the structural principles derived for OMPs of Escherichia coli. According to this mo del, sixteen polypeptide segments, which are highly conserved, travers e the outer membrane, thereby creating eight external loops, most of w hich are highly variable.