Structural & Molecular Virology

Bacteriophages (phages) are the most abundant and diverse biological entities on Earth. Yet, several aspects of their biology remain remarkably elusive. Our main research interest is to unravel the molecular mechanisms used by phages in the early steps of infection to recognize and bind to their specific hosts, and to inactivate the bacterial immune system CRISPR-Cas9. This will provide valuable fundamental knowledge to better understand phage-bacteria interactions and to pave the way for the rational development of phage-based applications for biocontrol, diagnostic and therapeutic purposes.

Host binding machineries

The first step in phage infection is recognition and binding to a specific host cell. Phages’ host-binding machineries are multiprotein nanodevices evolved to adapt to cell surface receptors. We and others have shown that siphophages’ host-binding machineries that bind to lactic acid bacteria cell wall polysaccharides are LEGO®-like assemblies highly diverse in their composition, architecture and function. Moreover, we have identified unique features in the host-binding machineries of phages infecting mycobacteria, which are likely adapted to the peculiar composition of their host cell wall.

What is the structural and functional diversity of host-binding devices?

Anti-CRISPR-Cas9 proteins

The endless battle for survival between phages and their hosts drives an evolutionary arms race with co-adaptation of their attack and defense mechanisms. In particular, phages have evolved highly diverse anti-CRISPR-Cas9 proteins (Acrs) to inactivate the bacterial CRISPR-Cas9 adaptative immunity and proliferate. We have described the molecular mechanism of AcrIIA6, an Acr identified in S. thermophilus virulent phages, which was the first example of a Cas9 allosteric inhibitor preventing cleavage of target DNA (the last step of CRISPR-Cas9 immunity). Interestingly, the first example of an Acr inhibiting the integration of viral DNA into the bacterial chromosome (the first step of CRISPR-Cas9 immunity) is a short version of AcrIIA6. Yet, the molecular mode of action of this truncated Acr remains unknown.

What is the structural and functional diversity of anti-CRISPR-Cas9 proteins.

Allosteric inhibitor that affects Cas9 structure and dynamics associated to DNA binding.