The fimbrial adhesin F17-G of enterotoxigenic Escherichia coli has an immunoglobulin-like lectin domain that binds N-acetylglucosamine.
The F17-G adhesin at the tip of flexible F17 fimbriae of enterotoxigenic Escherichia coli mediates binding to N-acetyl-beta-D-glucosamine-presenting receptors on the microvilli of the intestinal epithelium of ruminants. We report the 1.7 A resolution crystal structure of the lectin domain of F17-G, both free and in complex with N-acetylglucosamine. The monosaccharide is bound on the side of the ellipsoid-shaped protein in a conserved site around which all natural variations of F17-G are clustered. A model is proposed for the interaction between F17-fimbriated E. coli and microvilli with enhanced affinity compared with the binding constant we determined for F17-G binding to N-acetylglucosamine (0.85 mM-1). Unexpectedly, the F17-G structure reveals that the lectin domains of the F17-G, PapGII and FimH fimbrial adhesins all share the immunoglobulin-like fold of the structural components (pilins) of their fimbriae, despite lack of any sequence identity. Fold comparisons with pilin and chaperone structures of the chaperone/usher pathway highlight the central role of the C-terminal beta-strand G of the immunoglobulin-like fold and provides new insights into pilus assembly, function and adhesion.
Buts
Lieven
L
Department of Ultrastructure, Institute for Molecular Biology, Vrije Universiteit Brussel, Vlaams Interuniversitair Instituut voor Biotechnologie, Brussels, Belgium.
Bouckaert
Julie
J
De Genst
Erwin
E
Loris
Remy
R
Oscarson
Stefan
S
Lahmann
Martina
M
Messens
Joris
J
Brosens
Elke
E
Wyns
Lode
L
De Greve
Henri
H
D000117:Acetylglucosamine / Q000378:metabolism*; D018829:Adhesins, Bacterial / Q000737:chemistry* / Q000378:metabolism; D018830:Adhesins, Escherichia coli / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001422:Bacterial Adhesion / Q000502:physiology*; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D036781:Fimbriae Proteins / Q000737:chemistry / Q000378:metabolism; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D007700:Kinetics; D037102:Lectins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D029968:Escherichia coli Proteins; C478166:F17-G protein, E coli; D037102:Lectins; C092426:PapG protein, E coli; C058769:fimH protein, E coli; D036781:Fimbriae Proteins; D000117:Acetylglucosamine