Interaction of FimB and FimE with the fim switch that controls the phase variation of type 1 fimbriae in Escherichia coli K‐12

Abstract

The phase variation of type 1 fimbriae in Escherichia coli is associated with the site-specific inversion of a short DNA element. Recombination at fim requires fimB and fimE, and their products are considered to be the fim recombinases. In this study, FimB and FimE were overproduced and extracts containing the proteins were shown to (i) bind to and (ii) invert the fim switch in vitro. Phenanthroline-copper protection of DNA-protein complexes showed that both FimB and FimE bind to half-sites that flank, and overlap with, the left and right inverted repeats (IRL and IRR, respectively) of the fim switch. Alignment of the four half-sites identified a conserved 5'-CA doublet; mutation of these two bases lowers the affinity of binding of both FimB and FimE to the inverted repeats, and greatly diminishes inversion of the fim switch in vivo. The specificity of the fim recombinases observed in vivo (FimB switching in both directions; FimE switching from on-to-off only) was maintained in vitro. Furthermore, the different binding affinities of FimB and FimE for the various half-site combinations suggests that the specificity of FimE could arise, in part, from the low affinity of FimE for IRL (off).

Demonstration of regulatory cross-talk between P fimbriae and type 1 fimbriae in uropathogenic Escherichia coli

“…fused to the fim switch (pNJH97, Table 3). The fusion consists of the fim switch region flanked by both outside binding sites for the fim recombinases, inverted repeat left (IRL) OUT and inverted repeat right (IRR) OUT, resulting in a sequence of 346 bp (Gally et al, 1996). The responsiveness of this minimal fim switch unit to K-12 fim recombinases was confirmed in two ways.…”

“…The mechanisms that control the phase-variable expression are distinct, with type 1 fimbriae regulated by an invertible DNA element (fim switch), and P fimbriae by mutually exclusive protein complexes initiated by alternative DNA methylation patterns (Blomfield, 2001). Phase variation of type 1 fimbrial expression requires the activity of two recombinases; FimB promotes inversion in both directions, whereas FimE mediates predominantly on-to-off inversion (Gally et al, 1996;Klemm, 1986). Previous work has demonstrated that a regulator from the P-fimbrial gene cluster, PapB, when expressed from a plasmid, is able to prevent inversion of the fim switch (Holden et al, 2001;Xia et al, 2000).…”

The type 1 pili regulator gene fimX and pathogenicity island PAI-X as molecular markers of uropathogenic Escherichia coli

“…The orientation of the invertible type 1 pili promoter region (fimS) (Abraham et al, 1985) is determined by the action of multiple tyrosine recombinases. UPEC strains are known to possess up to five Fim-like tyrosine recombinases (FimB, FimE, FimX, IpuA and IpuB) based on sequence homology, and all but IpuB are have been shown to invert fimS (Bryan et al, 2006;Gally et al, 1996;Hannan et al, 2008;Klemm, 1986;McClain et al, 1991;Xie et al, 2006) with differing biochemical activities: FimE inverts the promoter from ON to OFF, FimB catalyses bidirectional inversion, but favours OFF to ON, IpuA also has bidirectional activity, while FimX is able to invert fimS from OFF to ON.…”

Regulation of type 1 fimbriae synthesis and biofilm formation by the transcriptional regulator LrhA of Escherichia coli

“…FimB facilitates inversion from phase-OFF to phase-ON, as well as inversion from phase-ON to phase-OFF. FimE, on the other hand, causes only switching from phase-ON to phase-OFF (Blomfield et al, 1991;Gally et al, 1996). In addition to the fim recombinases, efficient inversion of the fim switch requires the accessory proteins integration host factor (IHF) and leucine-responsive regulatory protein (Lrp) (Blomfield et al, 1993(Blomfield et al, , 1997Dorman & Higgins, 1987;Gally et al, 1994).…”