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Infection and Immunity, May 2000, p. 2638-2646, Vol. 68, No. 5
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

Mark A. Schembri,1 Evgeni V. Sokurenko,2 and Per Klemm1,*

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.

* 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.

Infection and Immunity, May 2000, p. 2638-2646, Vol. 68, No. 5
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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