Bacteroidales pore-forming toxins: unravelling receptor specificity

Details

Supervisors

Collet, Jean-François

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

The human gut microbiota is primarily composed of bacteria as well as other microorganisms that are important for host health by participating in energy metabolism and immunomodulation. Among these, Bacteroidales account for 50% of all Gram-negative bacteria present in the gut and are essential for shaping its composition and long-term stability. To this end, Bacteroidales engage in various host-microbe and microbe-microbe interactions. Specifically, Bacteroidales are endowed with a number of competition mechanisms that allow them to protect their ecological niche and fend off invaders. These include machineries such as the type 6 secretion system (T6SS) or the more recently discovered Bacteroidales-Secreted Antimicrobial Proteins (BSAPs). The latter represent a new class of Pore Forming Toxins (PFTs) and have been shown to possess potent bactericidal activity. Strikingly, BSAPs are highly selective and each one recognizes a specific receptor on the surface of a competitor cell. Cell death is achieved by the formation of a transmembrane lytic pore. To date, it remains unclear how BSAPs recognise their receptor and which domains are implicated in this process. Therefore, we focused on defining which molecular determinants provide this high selectivity by investigating the model proteins BSAP-1 and BSAP-4. Specifically, we tested the hypothesis that the BSAP C-terminal domain (CTD), the most variable region among BSAPs, is the key determinant for receptor specificity. To this end, we generated full-length and truncated versions of BSAP-1 and -4 and assessed their bactericidal activity both in vivo using competition assays and in vitro using sensitivity assays. In addition, we directly measured receptor-binding capacity of these proteins by performing pull-down experiments and fluorescence microscopy. Our results demonstrate that the CTD of BSAP-1 is required and sufficient for receptor recognition. Preliminary results indicate that this is also the case for BSAP-4, although this needs to be further investigated.