Evasion of Toll-like receptor 5 by flagellated bacteria

doi:10.1073/pnas.0502040102

Evasion of Toll-like receptor 5 by flagellated bacteria

^*Institute for Systems Biology, 1441 North 34th Street, Seattle, WA 98103; Departments of ^†Immunology, ^‡Pathology, ^§Laboratory Medicine, and ^¶Microbiology, University of Washington, 1959 Northeast Pacific Street, Seattle, WA 98195; and ^∥Institute for Biological Sciences, National Research Council, 100 Sussex Drive, Ottawa, ON, Canada K1A OR6

Edited by Ralph M. Steinman, The Rockefeller University, New York, NY, and approved April 26, 2005 (received for review March 11, 2005)

Abstract

Toll-like receptor 5 (TLR5) recognizes an evolutionarily conserved site on bacterial flagellin that is required for flagellar filament assembly and motility. The α and ε Proteobacteria, including the important human pathogens Campylobacter jejuni, Helicobacter pylori, and Bartonella bacilliformis, require flagellar motility to efficiently infect mammalian hosts. In this study, we demonstrate that these bacteria make flagellin molecules that are not recognized by TLR5. We map the site responsible for TLR5 evasion to amino acids 89-96 of the N-terminal D1 domain, which is centrally positioned within the previously defined TLR5 recognition site. Salmonella flagellin is strongly recognized by TLR5, but mutating residues 89-96 to the corresponding H. pylori flaA sequence abolishes TLR5 recognition and also destroys bacterial motility. To preserve bacterial motility, α and ε Proteobacteria possess compensatory amino acid changes in other regions of the flagellin molecule, and we engineer a mutant form of Salmonella flagellin that evades TLR5 but retains motility. These results suggest that TLR5 evasion is critical for the survival of this subset of bacteria at mucosal sites in animals and raise the intriguing possibility that flagellin receptors provided the selective force to drive the evolution of these unique subclasses of bacterial flagellins.

Footnotes

↵ ** To whom correspondence should be addressed. E-mail: aderem{at}systemsbiology.org.
Author contributions: E.A.-N. and K.D.S. designed research; E.A.-N., K.D.S., K.L.S., and S.L.R.B. performed research; E.A.-N. and K.D.S. analyzed data; B.T.C. and S.M.L. contributed new reagents/analytic tools; and E.A.-N., K.D.S., and A.A. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviation: TLR, Toll-like receptor.