Molecular characterization of a 40‐kDa outer membrane protein, FomA, of Fusobacterium periodonticum and comparison with Fusobacterium nucleatum

Abstract

The 40 kDa-outer membrane protein FomA of Fusobacterium periodonticum ATCC 33693 was found to exhibit heat modifiable properties, typical for a porin, and N-terminal sequencing indicated a close relationship to the porin FomA of Fusobacterium nucleatum. A polymerase chain reaction approach was therefore applied for sequencing the fomA gene of F. periodonticum, and nucleotide and deduced amino acid sequences were aligned 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 similarity with the F. nucleatum gene. The transcriptional unit of FomA, on the other hand, was very similar, with the similarities concentrated in domains that were interspersed with hypervariable regions. A topology model was made and compared with those made for F. nucleatum. This indicated that the great similarities reside in the membrane-spanning segments of the protein, while most cell surface exposed loops were hypervariable. The results strongly support the proposed model for FomA and also indicate that these taxa are related but on a lower level than the subspecies level. The codon usage of F. periodonticum is comparable to that of F. nucleatum, and the triplet AGA is the only codon used for arginine.

Structural characterization of the fusobacterial non-specific porin FomA suggests a 14-stranded topology, unlike the classical porins

“…Furthermore, the thermal melting profiles suggest that the FomA protein possesses a β-barrel architecture typical for OMPs (Schulz, 2000), since the cooperative unfolding transition occurs at high temperatures ( 80 mC), reflecting the very stable three-dimensional structures of these proteins. The evidence for a β-barrel architecture is in line with the published topology model for the FomA protein suggesting that the FomA protein is a 16-stranded β-barrel (Bolstad et al, 1994(Bolstad et al, , 1995. The apparent lower content of secondary structure observed with the rFomA "!…”

Identification and Characterization of a Novel Adhesin Unique to Oral Fusobacteria

“…It is not unusual for a membrane protein to have aberrant migration on SDS-PAGE. For instance, the 40-kDa FomA protein has been reported to migrate as 37-kDa, 40-kDa, 42-kDa, and 62-kDa proteins (5,34,35).…”

Topological investigations of the FomA porin from Fusobacterium nucleatum and identification of the constriction loop L6 The GenBank accession number for the sequence reported in this paper is X72583.

“…The deduced amino acid sequence from four different fomA genes showed no sequence similarity to other proteins (Bolstad et al, 1994(Bolstad et al, , 1995. However, the topology model of FomA (Bolstad et al, 1994), based on structure-prediction principles derived from E. coli outer-membrane proteins, indicates that FomA shares several structural features with the porins of other Gram-negative bacteria (Cowan et al, 1992 ;Weiss & Schulz, 1992).…”

“…However, the topology model of FomA (Bolstad et al, 1994), based on structure-prediction principles derived from E. coli outer-membrane proteins, indicates that FomA shares several structural features with the porins of other Gram-negative bacteria (Cowan et al, 1992 ;Weiss & Schulz, 1992). The FomA monomer is proposed to fold as a 16-stranded antiparallel β-barrel with eight loops exposed to the exterior (Bolstad et al, 1994(Bolstad et al, , 1995. Most of these regions correspond to the most hydrophilic and variable regions among the fusobacterial porins, and we have recently demonstrated the surface exposure of six of the predicted loops by insertion mutagenesis (Puntervoll et al, 2000).…”