Autotransporter (AT) proteins which are the largest group of surface adhesins in Gram-negative bacteria. These proteins play a central role in controlling bacterial interactions. They allow bacteria to aggregate with other bacteria, adhere to human cells, and form biofilms – all key facilitators of pathogenesis. Despite their abundance and critical roles in pathogenesis, to date the mechanisms of action and structures of less than 0.008% of the total ATs have been investigated.
We have developed a multidisciplinary framework that combines X-ray crystallography, biophysical techniques, immunoassays and cellular assays to investigate AT function. This has resulted in the determination of the first structure and mode of action of an AIDA-I-type AT protein (representative of the largest group in the AT family). This investigation revealed that a ‘head to tail’ self-association of the AT Antigen 43 (Ag43) between neighbouring cells promoted bacterial aggregation and biofilm formation.
We have produced the structures of a further seven AT proteins, which alone will comprise a third of the total AT structures in the PDB. More importantly, we are now starting to elucidate the mechanisms of action for diverse ATs. So far, we have found that different AT adhesins promote bacterial aggregation using subtle variations in this self-association mechanism compared to Ag43. We are also starting to uncover how AT adhesins bind epithelial surfaces, which is revealing new modes of protein-protein and protein-carbohydrate interactions. Furthermore, we are breaking new ground towards understanding how the functions of AT adhesins are regulated. Finally, we are using this knowledge to successfully develop methods for disrupting AT function.