Autotransporter proteins (AT) are the most common family of secreted and outer membrane proteins in Gram-negative bacteria where they play a critical role in pathogenesis. These proteins are characterised by a conserved domain architecture, which consists of a signal peptide at the N-terminus, an α-domain and a β-domain on the C-terminus. The signal peptide controls transport from the inner membrane to the periplasm, while the β-domain translocates the functional α-domain to the cell surface.
AT proteins can be grouped into three major categories: esterases (i), serine protease ATs of Enterobacteriaceae (SPATES) (ii) and AIDA-I-type ATs (Adhesins or Self-associating ATs (SAATs) (iii). The latter group is the most abundant and is associated with different virulence functions including cell adhesion, aggregation and biofilm formation. One of the better-characterised AIDA-I-type AT is Antigen 43 (Ag43), which is present in both pathogenic and non-pathogenic E. coli strains. 

Our work on Ag43a from uropathogenic E. coli has shown that bacterial cells are covered by Ag43 proteins, that behave like a molecular Velcro, attaching cells together to form bacterial cell clusters.
This work aims to develop a strategy to block Ag43a function and the associated formation of persistent and intrinsically resistant bacterial communities. This will be achieved by screening Ag43a against a shark single variable new antigen receptor domain antibody fragment (vNAR) library using phage display technology. The best vNAR will be tested for their ability to inhibit Ag43-mediated aggregation and biofilm formation. The precise mechanism of interaction with Ag43a will be examined by co-crystallisation with the most promising antibody.