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Infection and Immunity, May 2000, p. 2638-2646, Vol. 68, No. 5
Department of Microbiology, Technical
University of Denmark, DK-2800 Lyngby,
Denmark,1 and Department of
Microbiology, University of Washington, Seattle, Washington
981952
Received 30 November 1999/Returned for modification 12 January
2000/Accepted 3 February 2000
Type 1 fimbriae are surface organelles of Escherichia
coli which mediate D-mannose-sensitive binding to
different host surfaces. This binding is conferred by the minor
fimbrial component FimH. Naturally occurring variants of the FimH
protein have been selected in nature for their ability to recognize
specific receptor targets. In particular, variants that bind strongly
to terminally exposed monomannose residues have been associated with a
pathogenicity-adaptive phenotype that enhances E. coli
colonization of extraintestinal locations such as the urinary bladder.
In this study we have used random mutagenesis to specifically identify
nonselective mutations in the FimH adhesin which modify its binding
phenotype. Isogenic E. coli clones expressing FimH variants
were tested for their ability to bind yeast cells and model
glycoproteins that contain oligosaccharide moieties rich in either
terminal monomannose, oligomannose, or nonmannose residues. Both the
monomannose- and the oligomannose-binding capacity of type 1 fimbriae
could be altered by minor amino acid changes in the FimH protein. The
monomannose-binding phenotype was particularly sensitive to changes,
with extensive differences in binding being observed in comparison to
wild-type FimH levels. Different structural alterations were able to
cause similar functional changes in FimH, suggesting a high degree of flexibility to target recognition by this adhesin. Alteration of
residue P49 of the mature FimH protein, which occurs within the
recently elucidated carbohydrate-binding pocket of FimH, completely abolished its function. Amino acid changes that increased the binding
capacity of FimH were located outside receptor-interacting residues,
indicating that functional changes relevant to pathogenicity are likely
to be due to conformational changes of the adhesin.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Functional Flexibility of the FimH Adhesin:
Insights from a Random Mutant Library
*
Corresponding author. Mailing address: Department of
Microbiology, Bldg. 301, Technical University of Denmark, DK-2800
Lyngby, Denmark. Phone: 45-45-25-25-06. Fax: 45-45-93-28-09. E-mail:
impk{at}pop.dtu.dk.
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