Structural analyses of carbohydrate receptors for enterotoxins and adhesins of enterotoxigenic Escherichia coli

Abstract: Carbohydrate-binding proteins expressed by microbes are key determinants in initiating and sustaining infections that account for millions of deaths each year. This thesis fo- cused on proteins integral to infections instigated by enterotoxigenic Escherichia coli (ETEC); estimated as the largest bacterial cause of diarrhea in the world with hundreds of millions of cases each year. ETEC infections are mediated by two primary carbohy- drate-binding proteins; 1) Colonization factors (CF), which facilitate host cell attach- ment, and 2) Enterotoxins, which penetrate host cells to induce a potentially lethal diar- rheal response. By employing biochemical techniques, such as chromatogram binding assays, mass spectrometry and NMR, we dissected the precise mechanisms fundamental for the interactions of ETEC carbohydrate-binding proteins. In the presented papers, the novel colonization factor CS30, and the enterotoxins LT- IIb, and LT-IIc where investigated. Our findings identified the sulfatide glycosphin- golipid as the principal receptor for CS30 and emphasized the significance of the car- bohydrate-presenting lipid moiety in binding. The diarrhea-inducing toxins, LT-IIb and LT-IIc, demonstrated distinct binding specificity to sialic acid presenting glycosphin- golipids, and the presence of such receptors were confirmed in the human intestine. Lastly, structural studies detailed the atomic framework of these binding interactions and quantified the binding affinities. By revealing the specific carbohydrate interactions underpinning both adhesion and toxin action, our study uncovers the intricate processes governing pathogenic infection mechanisms, which may inform the design of next-generation anti-bacterial therapeu- tics, vaccines and diagnostical tools.