Abstract

The tolerance of pathogenic strains or their clearance is covered by many immune cell receptors such as Pathogen Recognition Receptors (PRRs) including C-type lectin receptors (CLRs) that specifically interact with carbohydrates moieties. Lipopolysaccharide (LPS), expressed on the surface of bacteria, presents  one  of  the  signatures  of  Gram-negative  by  being  both  a  structural  and  recognition  motif  by  the host cell. The molecular diversity of both LPS (i.e. various carbohydrates, lengths and heterogeneity levels) and lectins (variable binding sites architectures) would confer them the particularity of controlling variable situations and targeting specific interactions. Investigating LPS-Lectins interactions is challenging and requires an interdisciplinary approach. On the above basis, we sought to investigate the interaction between a C-type lectin i.e. human Macrophage Galactose-type Lectin MGL and LPSs (from E. coli R1, R3 mutants and E. coli O157:H7 strain). The difficult experimental handling of such native biomolecules directed the use of a divided set of approaches. Our scientific strategy includes the use of Nuclear Magne-tic Resonance NMR spectroscopy, fluorescence microscopy, and molecular binding essays. By combining these methods, we demonstrated that the Extracellular Domain (ECD) of MGL strongly and specifically interacts with E. coli R1 glycoconjugates at the surface of bacteria through its terminal di-galactose motif. The contribution of a putative secondary binding site on the Carbohydrate Recognition Domain (CRD) of MGL in E. coli glycoconjugates recognition remains to be investigated. This PhD work showed that, des-pite the difficulties that such large system studies may encounter, many findings are attainable by using our scientific strategy. The possibility of investigating data from atomic to cellular scale on LPS-lectin inte-ractions in either modified or native states, opens prominent horizons for the study of bacterial infections.