Plasma proteins glycosylation and its alteration in disease

Most plasma proteins are glycoproteins, that is, they possess oligosaccharide chains attached to the polypeptide core. These oligosaccharides have important structural and functional roles; they serve as recognition markers (ligands), especially for lectin receptors, thus modulating the glycoprotein interactions. Protein glycosylation is a posttranslational event which depends on the proteic core and biosynthetic cell type and results in a set of microheterogeneous forms (glycoforms) of an individual glycoprotein. Under pathological conditions an alteration of the glycosylation pattern of plasma glycoproteins occurs. So, degalactosylated IgG and IgA1 detected in rheumatoid arthritis and IgA nephropathy, respectively, are implicated in the pathogenic mechanisms. Alteration of transferrin, alpha 1-acid glycoprotein and alpha-fetoprotein glycosylation (reduced sialylation and increased branching of oligosaccharide chains) occurs in liver diseases. In inflammations and infections the alteration is dependent on the disease studied, while increased sialylation and fucosylation of acute-phase proteins are detected in cancer sera. Lectin-based methods have been developed for clinical purposes, in order to improve the diagnosis, prognosis evaluation, or treatment monitoring.