Uropathogenic Escherichia coli (UPEC) is the major etiological agent of urinary tract infections (UTIs) in the developed world. UPEC strains elaborate a multitude of virulence factors that contribute to their persistence within the urinary tract. Autotransporter (AT) proteins represent an important group of virulence factors that have been shown to mediate adhesion, invasion and biofilm formation. We have previously identified and characterized UpaB, an AT adhesion from UPEC that mediates its binding to fibronectin, fibrinogen, and laminin, and contributes to early colonization of the mouse bladder (1). Our in silico analysis revealed that the upaB gene is highly prevalent in a collection of UPEC clinical strains (32/45; 71%) isolated from urospesis patients. We detected high UpaB antibody titers in the corresponding blood plasma from these urosepsis patients, demonstrating the strong immunogenicity of UpaB and further suggesting it plays an important role during UPEC infection. We have determined the crystal structure of the effector domain of UpaB (αUpaB) at 1.9 Å resolution. Our αUpaB structure reveals a unique three-stranded β-helix comprising three defined sections: a central domain composed of long β-strands which form an unusually wide β-helix that protrudes from the helical core and two flanking β-helical domains similar to previously characterized β-helical proteins. Our enzyme-linked immunosorbent assay results suggest that the binding of UpaB to human fibronectin is mediated by the central β-helix protusion of UpaB. The elucidation of the structure-function relationship of UpaB will allow the molecular understanding of its specific roles in pathogenesis and could provide a basis for the design and development molecules that inhibit its function.
1. Allsopp LP, et al. 2012. Molecular characterization of UpaB and UpaC, two new autotransporter proteins of uropathogenic Escherichia coli CFT073. Infect. Immun. 80:321–332.