Epithelial mucins and bacterial adhesion Florent Colomb, Catherine Robbe-Masselot, Sophie Groux-Degroote, Julie Bouckaert, Philippe Delannoy* and Jean-Claude Michalski DOI: 10.1039/9781849739986-00596 Mucins are high molecular weight glycoproteins characterized by highly O-glycosylated tandem repeat domains. Mucin-type O-glycans exhibit a variety of terminal sequences including histo-blood group antigens that serve as counter receptors and participate in the adhesion and clearance of numerous bacteria including pathogens. In parallel, the pathological changes of mucin glycosylation modulate bacterial adhesion, often enhancing the adhesion of pathogenic bacteria. This review summarizes the current knowledge on the structure and biosynthesis of epithelial mucin O-glycans chains, the physio-pathological glycosylation repertoire of mucins and the role of mucin glycosyla- tion in bacterial adhesion, focusing on the gastrointestinal tract and airway mucins. 1 Introduction Mucins are major components of mucus and apical cell membranes of epithelia. They are high molecular weight glycoproteins characterized by the presence in the protein backbone of tandem repeat domains highly O-glycosylated onto serine and threonine residues. The O-glycan chains contribute to maintain the extended structure of mucins, conferring their rheological and biological properties essential for their protective functions. Mucin-type O-glycan chains are extremely diversified and exhibit a large number of terminal histo-blood group antigens that can serve as counter receptors for a large set of bacteria and participate to the adhesion and clearance of pathogens. The glycosylation of mucins is also modified in pathological conditions and the change of glyco-epitopes at the surface of epithelia modulates bacterial adhesion, thereby most often enhancing the adhesion of pathogenic bacteria. In this review, we summarize our current knowledge on the structure and biosynthesis of epithelial mucin O-glycans chains, the tissue and physio-pathological specific glycosylation repertoire of mucins and the role of epithelial mucins in bacterial adhesion, focusing on glycosylation of gastrointestinal and airway mucins, which are the main mucins exposed to bacteria. 2 Structure of epithelial mucin O-glycans 2.1 Secreted and cell surface mucins Mucins are the major structural components of mucus, a thick gelatinous fluid secreted by specialized epithelial cells such as goblet cells that covers and protects many human organs. Mucins are responsible for the rheological properties of mucus and are very high molecular weight UGSF, CNRS, UMR 8576, Univ. Lille Nord de France, USTL, Ba ˆtiment C9, F-59650 Villeneuve d’Ascq, France. E-mail: philippe.delannoy@univ-lille1.fr; jean-claude.michalski@univ-lille1.fr 596 | Carbohydr. Chem. , 2014, 40, 596–623  c The Royal Society of Chemistry 2014