A Review on the Roles of Potein Glycosylation in Balancing the Complement System

Abstract

The complement system is one of the earliest defense mechanisms that pathogens encounter. This ancient system consists of a cascade of glycoproteins that leads to cell lysis and labelling of pathogens or compromised host cells for immune response and phagocytosis. Nearly all complement proteins are modified with glycans. Glycosylation is one of the most common, but also one of the most complex protein modifications. Glycans can play major roles in protein folding, protein orientation, kinetics, and activity. While the structures and functions of glycans in the complement system have been studied broadly, many unresolved questions remain. Developments in glycan analysis methods and functional assays gradually improves the knowledge and characterization of complement glycoproteins in the last few years, but further developments will be required to study this system in detail. This review evaluates the current state of the art concerning glycosylation of major complement proteins, and provides a brief introduction on both glycosylation and the complement system. From this broad overview, several complement glycoproteins will be highlighted for their interesting characteristics and functions.