Structure of CFA/I fimbriae from enterotoxigenic Escherichia coli.
Adhesion pili (fimbriae) play a critical role in initiating the events that lead to intestinal colonization and diarrheal disease by enterotoxigenic Escherichia coli (ETEC), an E. coli pathotype that inflicts an enormous global disease burden. We elucidate atomic structures of an ETEC major pilin subunit, CfaB, from colonization factor antigen I (CFA/I) fimbriae. These data are used to construct models for 2 morphological forms of CFA/I fimbriae that are both observed in vivo: the helical filament into which it is typically assembled, and an extended, unwound conformation. Modeling and corroborative mutational data indicate that proline isomerization is involved in the conversion between these helical and extended forms. Our findings affirm the strong structural similarities seen between class 5 fimbriae (from bacteria primarily causing gastrointestinal disease) and class 1 pili (from bacteria that cause urinary, respiratory, and other infections) in the absence of significant primary sequence similarity. They also suggest that morphological and biochemical differences between fimbrial types, regardless of class, provide structural specialization that facilitates survival of each bacterial pathotype in its preferred host microenvironment. Last, we present structural evidence for bacterial use of antigenic variation to evade host immune responses, in that residues occupying the predicted surface-exposed face of CfaB and related class 5 pilins show much higher genetic sequence variability than the remainder of the pilin protein.
Li
Yong-Fu
YF
Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4256, USA.
Poole
Steven
S
Nishio
Kazuya
K
Jang
Ken
K
Rasulova
Fatima
F
McVeigh
Annette
A
Savarino
Stephen J
SJ
Xia
Di
D
Bullitt
Esther
E
D000942:Antigens, Bacterial / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D001665:Binding Sites; D018360:Crystallography, X-Ray; D054307:Enterotoxigenic Escherichia coli / Q000737:chemistry* / Q000235:genetics; D004927:Escherichia coli Infections / Q000276:immunology / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics; D036781:Fimbriae Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D008958:Models, Molecular; D009154:Mutation; D011392:Proline / Q000737:chemistry / Q000235:genetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics
D000942:Antigens, Bacterial; D029968:Escherichia coli Proteins; D021122:Protein Subunits; C022924:colonization factor antigens; D036781:Fimbriae Proteins; D011392:Proline