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.

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

“…This model was largely confirmed by the demonstration of the surface exposure of loops L3 to L7 by epitope insertion mutagenesis (Puntervoll et al, 2000), together with the fact that deletions in loops L1 to L7 did not impede the pore function (Kleivdal et al, 2001). In addition, deletions made in loop L6 led to a marked increase in the uptake of antibiotics through the FomA porin (Kleivdal et al, 2001), suggesting that this loop may function analogously to the pore constriction loop L3 of the structured non-specific porins of E. coli and Rhodobacter capsulatus (Cowan, 1993). Furthermore, a cluster of arginines that contributes to the constriction of the pore has been identified, similar to the cluster observed in the matrix porin OmpF of E. coli, but positioned closer to the C terminus (Kleivdal et al, 1999).…”

“…A topology model, suggesting that the FomA protein possesses the general topology of the non-specific porins, has been proposed on the basis of structural principles derived for OMPs of E. coli (Bolstad et al, 1994). This model was largely confirmed by the demonstration of the surface exposure of loops L3 to L7 by epitope insertion mutagenesis (Puntervoll et al, 2000), together with the fact that deletions in loops L1 to L7 did not impede the pore function (Kleivdal et al, 2001). In addition, deletions made in loop L6 led to a marked increase in the uptake of antibiotics through the FomA porin (Kleivdal et al, 2001), suggesting that this loop may function analogously to the pore constriction loop L3 of the structured non-specific porins of E. coli and Rhodobacter capsulatus (Cowan, 1993).…”

“…Earlier work has demonstrated that it is possible to replace residues 8 to 23 with the residues RS without the loss of pore function (Kleivdal et al, 2001), suggesting that this segment is not critical for maintaining the β-barrel structure of the FomA protein. In support of this is also the fact that the 37 kDa trypsin fragment of the FomA (FomA "!…”

“…Furthermore, a cluster of arginines that contributes to the constriction of the pore has been identified, similar to the cluster observed in the matrix porin OmpF of E. coli, but positioned closer to the C terminus (Kleivdal et al, 1999). We recently proposed that these structural deviations from the well-known porins may imply that FomA belongs to a separate subgroup of non-specific porins, reflecting the evolutionary distance between the fusobacteria and the proteobacteria (Kleivdal et al, 2001), but further structural information is clearly needed to establish whether this actually is the case. In the present study, we present the first physicochemical evidence that FomA is a β-barrel, and examine the role of the proposed loop L1.…”

The Major Outer Membrane Protein of Fusobacterium nucleatum (FomA) Folds and Inserts into Lipid Bilayers via Parallel Folding Pathways

“…Western blot analysis of recombinant FomA isolated from outer membranes of E. coli in native form indicated the presence of monomers. 25,35 These studies also showed that FomA trimers do not appear in SDS-polyacrylamide gels, even if the samples are not boiled before electrophoresis. 25 Possibly FomA trimers are formed, but are not very stable.…”