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Mucins and mucin-like molecules are highly O-glycosylated proteins present on the cell surface of mammals and other organisms. These glycoproteins are highly diverse in the apoprotein and glycan cores and play a central role in many biological processes and diseases. Mucins are the most abundant macromolecules in mucus and are responsible for its biochemical and biophysical properties. Mucin-like molecules cover various protozoan parasites, fungi and viruses. In humans, modifications in mucin glycosylation are associated with tumors in epithelial tissue. These modifications allow the distinction between normal and abnormal cell conditions and represent important targets for vaccine development against some cancers. Mucins and mucin-like molecules derived from pathogens are potential diagnostic markers and targets for therapeutic agents. In this review, we summarize the distribution, structure, role as immunomodulators, and the correlation of human mucins with diseases and perform a comparative analysis of mucins with mucin-like molecules present in human pathogens. Furthermore, we review the methods to produce pathogenic and human mucins using chemical synthesis and expression systems. Finally, we present applications of mucin-like molecules in diagnosis and prevention of relevant human diseases.

The genetic set up and the enzymes that define the O-glycosylation sites and transfer the activated sugars to the cell wall protein backbone have remained unknown for a long time. We are now beginning to see the emerging components of the molecular machinery that assembles these complex O-glycoproteins on the plant cell wall. Genes conferring the posttranslational modifications, i.e. proline hydroxylation and subsequent O-glycosylation, of the plant cell wall protein extensin subgroup have being recently identified. In this review we summarize the enzymes that define the O-glycosylation sites on the O-glycoproteins, i.e. the prolyl 4–hydroxylases (P4Hs), the glycosyltransferases that transfer arabinose units (named arabinosyltransferases, AraTs) and the one responsible for the transfer of a single galactose (galactosyltransferase, GalT) on the protein extensin backbones, and finally the EXT peroxidase-mediated crosslinking at the cell wall. We discuss the effect of posttranslational modification on the structure and function of extensins in the plant cell walls.