Abstract

Lectins are ubiquitous proteins that can reversibly and specifically bind to carbohydrates. Carbohydrate-mediated recognition and adhesion are key events in the early steps of interaction of pathogenic or symbiotic bacteria with a host. For example, Pseudomonas aeruginosa is an opportunistic bacterium that causes lethal lung infection in cystic fibrosis patients. Photorhabdus luminescens lives in a symbiotic relationship with nematodes and is involved in insecticidal activities of these worms. Both bacteria produce several lectins, i.e. glycan receptors, which are specific for the host glycoconjugates.
The aim of this PhD thesis was to use neutron protein crystallography to provide insights into lectin-carbohydrate interactions involved in bacterial infection. Fucose-specific lectins PLL and LecB from Photorhabdus luminescens and Pseudomonas aeruginosa, respectively, were produced in perdeuterated forms and crystallized with a ligand. A unique part of the thesis was the in vivo production of a perdeuterated monosaccharide, L-fucose, using genetically modified strains of E. coli bacteria designed by Dr. Eric Samain at CERMAV institute in Grenoble. Perdeuterated fucose has been successfully produced, purified and biophysically characterized. It was used as a ligand for crystallization trials of both PLL and LecB lectins.
Using neutron protein crystallography, we have unraveled the details of protein-carbohydrate interactions in two fucose-specific lectins. PLL lectin from bacteria Photorhabdus luminescens was chosen as a model system for detailed description of H-bonding network involved in sugar recognition, including direct and water-bridged hydrogen bonds and CD-? stacking interactions between the apolar face of fucose and aromatic amino acids. LecB lectin from Pseudomonas aeruginosa, a human opportunistic pathogen that causes lethal infections in cystic fibrosis patients, is currently viewed as a potential drug target for glycomimetic compounds with antiadhesive properties. LecB displays an unusually high affinity towards fucose and our neutron study enabled a complete description of the hydrogen-bonding network and the protonation state of charged amino acids involved in the sugar-binding.

Given the health context, the number of places in the room is limited.
Zoom link to be asked from : anne.imberty(at)cermav.cnrs.fr