Repeats-In-Toxin Adhesion Proteins: What Makes Them Stick?
Bacteria use adhesion proteins (adhesins) to bind substrates on biotic and abiotic surfaces to initiate biofilm formation. These bacterial communities can be detrimental to a host when, for example, they cause teeth plaques, chronic infections, and the contamination of food products. On the other hand, they can also promote plant growth and the degradation of oils, depending on the organism. Characterizing adhesin interactions may present opportunities to inhibit destructive biofilms and reinforce the advantageous ones. A subgroup of these proteins called Repeats-In-Toxin adhesins are exported by a type 1 secretion system and are retained on the outer membrane of some Gram-negative bacteria. This thesis examined C-terminal ligand-binding domains from three different adhesins: 1) The large adhesion protein from the oil- degrading bacterium Marinobacter hydrocarbonoclasticus, contains a PA14 domain with the ability to bind specific carbohydrates. This 20-kDa domain was tested as a dextran-affinity tag for purification of recombinant proteins on dextran-based size-exclusion resins. The tag bound to Superdex, Sephadex, and Sephacryl, and proved to be superior to nickel-affinity chromatography. 2) A medium adhesion protein from Pseudomonas fluorescens, which contributes to biofilm formation on plant root surfaces, contains a von Willebrand Factor A domain in the C-terminal region that was characterized by X-ray crystallography. While human integrin contains a homologue of this domain to bind extracellular matrix proteins, including collagen, the binding partner for Pseudomonas fluorescens is still unknown. Lastly, 3) the flagellum-regulated hemagglutinin A, which binds to epithelial cells and erythrocytes in the pathogenic lifecycle of Vibrio cholerae, does so through a peptide-binding domain. This protein was produced with its neighboring domain and co-crystallized with nanomolar-affinity pentapeptide ligands. These peptides successfully inhibited attachment of V. cholerae to erythrocytes and could potentially be used for anti-adhesion therapy against cholera.