Integrated regulatory responses of fimB to N-acetylneuraminic (sialic) acid and GlcNAc in Escherichia coli K-12

^*Department of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, United Kingdom; and ^†Institut de Biologie Physico-Chimique (Unité Propre de Recherche 9073, Centre National de la Recherche Scientifique), 13 Rue Pierre et Marie Curie, 75005 Paris, France

Edited by Sydney Kustu, University of California, Berkeley, CA, and approved October 6, 2004 (received for review August 9, 2004)

Abstract

Bacterial-host attachment by means of bacterial adhesins is a key step in host colonization. Phase variation (reversible on-off switching) of the type 1 fimbrial adhesin of Escherichia coli involves a DNA inversion catalyzed by FimB (switching in either direction) or FimE (mainly on-to-off switching). fimB is separated from the divergent yjhATS operon by a large (1.4 kbp) intergenic region. Short (≈28 bp) cis-active elements (regions 1 and 2) close to yjhA stimulate fimB expression and are required for sialic acid (Neu₅Ac) sensitivity of its expression [El-Labany, S., Sohanpal, B. K., Lahooti, M., Akerman, R. & Blomfield, I. C. (2003) Mol. Microbiol. 49, 1109-1118]. Here, we show that whereas NanR, a sialic acid-response regulator, binds to region 1, NagC, a GlcNAc-6P-responsive protein, binds to region 2 instead. The NanR- and NagC-binding sites lie adjacent to deoxyadenosine methylase (Dam) methylation sites (5′-GATC) that are protected from modification, and the two regulators are shown to be required for methylation protection at regions 1 and 2, respectively. Mutations in nanR and nagC diminish fimB expression, and both fimB expression and FimB recombination are inhibited by GlcNAc (3- and >35-fold, respectively). Sialic acid catabolism generates GlcNAc-6-P, and whereas GlcNAc disrupts methylation protection by NagC alone, Neu₅Ac inhibits the protection mediated by both NanR and NagC as expected. Type 1 fimbriae are proinflammatory, and host defenses enhance the release of both Neu₅Ac and GlcNAc by a variety of mechanisms. Inhibition of type 1 fimbriation by these amino sugars may thus help balance the interaction between E. coli and its hosts.

type 1 fimbriae

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: i.c.blomfield{at}kent.ac.uk..
Author contributions: B.K.S., S.E.-L., J.A.P., and I.C.B. designed research; B.K.S., S.E.-L., and J.A.P. performed research; B.K.S., S.E.-L., M.H., and J.A.P. contributed new reagents/analytic tools; B.K.S., S.E.-L., J.A.P., and I.C.B. analyzed data; and B.K.S., J.A.P., and I.C.B. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: Rm1 or Rm5, region 1 or 5 mutation; EMSA, electrophoretic mobility-shift assay; RD, rich-defined medium; Dam, deoxyadenosine methylase.
Freely available online through the PNAS open access option.