Date of Award
4-10-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Gram-negative bacteria can cause a variety of human infectious diseases, and urinary tract infections (UTIs) are a common disease type caused by these bacteria. Such infections predominantly affect women and are frequently recurrent. UTIs are becoming more difficult to treat due to increasing antibiotic resistance. Thus, in order to develop new anti-virulence strategies, we must gain greater insight into the virulence factors which contribute to uropathogenesis. Gram-negative bacteria use chaperone usher pathway (CUP) pili, tipped with adhesive proteins, called adhesins, to mediate host tissue adherence in particular and uropathogenesis in general. CUP pili are phylogenetically organized into distinct clades. The gamma-4 clade is composed of pili from a variety of Gram-negative genera, including Acinetobacter and uropathogenic Escherichia. A. baumannii makes use of two gamma-4 pili, Abp1 and Abp2, in combination to colonize the fibrinogen-coated catheter and bladder in a mouse model of A. baumannii catheter-associated urinary tract infection (CAUTI). These two pili contribute, to varying degrees, to A. baumannii biofilm formation. The tip adhesins of these pili, Abp1D and Abp2D, are able to bind fibrinogen, an important host protein in CAUTI pathogenesis, and collagen IV, a ubiquitous host xiii glycoprotein. Molecularly, they bind overlapping receptors. The crystal structures of Abp1D and Abp2D were solved and reveal highly structurally similar proteins. Their binding pockets contain a conserved anterior loop motif which is flexible and has the ability to open and close the pocket. This is regulated by an intramolecular interaction between residues on the underside of the anterior loop. Disruption of this interaction favors a closed pocket conformation in silico and increases the binding affinity of the protein. In uropathogenic E. coli, the gastrointestinal (GI) tract serves as a reservoir for UTIs, and uropathogenic E. coli uses CUP pili to mediate GI tract colonization. The Yeh pilus contributes to GI tract colonization fitness through the binding of GI tract luminal contents. In particular, the Yeh pilus adhesin, YehD, binds to pectin, a complex polysaccharide contained within plant material. The Yeh crystal structure reveals a receptor binding domain core and a novel alpha-helical flap motif that runs the length of the core. A hydrophobic region at the distal end of the flap contributes to holding it in a tucked conformation. Furthermore, a preliminary comparative study of the Yeh, S, Yqi, and F17-like pilus rods revealed CUP pilus rod quaternary structural diversity, with the gamma-4 Yeh and F17-like pili exhibiting a zigzag helical rod motif, demonstrating that this quaternary structure motif is present within classical CUP pili. This work has contributed to our understanding of the structural and functional diversity of gamma-4 CUP pili and their roles in Gram-negative infection and colonization.
Language
English (en)
Chair and Committee
Scott Hultgren
Recommended Citation
Tamadonfar, Kevin Omeed, "The structural biology of gamma-4 CUP pili" (2024). Arts & Sciences Electronic Theses and Dissertations. 3064.
https://openscholarship.wustl.edu/art_sci_etds/3064