Abstract
O-Glycosylation is one of the most important posttranslational modifications of proteins. It takes part in protein conformation, protein sorting, developmental processes and the modulation of enzymatic activities. In vertebrates, the basics of the biosynthetic pathway of O-glycans are already well understood. However, the regulation of the processes and the molecular aspects of defects, especially in correlation with cancer or developmental abnormalities, are still under investigation. The knowledge of the correlating invertebrate systems and evolutionary aspects of these highly conserved biosynthetic events may help improve the understanding of the regulatory factors of this pathway. Invertebrates display a broad spectrum of glycosylation varieties, providing an enormous potential for glycan modifications which may be used for the design of new pharmaceutically active substances. Here, overviews of the present knowledge of invertebrate mucin-type O-glycan structures and the currently identified enzymes responsible for the biosynthesis of these oligosaccharides are presented, and the few data dealing with functional aspects of O-glycans are summarised.
Highlights
Protein glycosylation plays an important role in several types of recognition processes ranging from fertilisation and development to pathological events and cell death. 30 years ago, the role of O-glycans was only seen in the influence of physical parameters, such as ensuring protein stability and tertiary structure, providing the basis for rigid conformations and slowing down proteolytic degradation of the peptide chain; most of specialised recognition events have been allocated to N-glycans. It is Molecules 2015, 20 clear that different types of O-glycans are relevant for many more functions, such as modulating of enzyme activity (e.g., the reversible attachment of an O-linked GlcNAc (N-acetylglucosamine) residue to cytoplasmic and nuclear proteins), modulating pro-protein processing and acting as signal molecules or sorting determinants guiding the modified protein in the cell from the place of biosynthesis to its target location [1,2,3,4]
Biosynthesis begins in the endoplasmic reticulum by forming a highly conserved oligosaccharide structure (two GlcNAc, nine Man, three Glc residues) on a lipid precursor
Fuc is a common feature in terminal position of all animals, but it seems to be more dominant in invertebrates; multifucosylated and further elongated
Summary
Protein glycosylation plays an important role in several types of recognition processes ranging from fertilisation and development to pathological events and cell death. 30 years ago, the role of O-glycans was only seen in the influence of physical parameters, such as ensuring protein stability and tertiary structure, providing the basis for rigid conformations and slowing down proteolytic degradation of the peptide chain; most of specialised recognition events have been allocated to N-glycans. 30 years ago, the role of O-glycans was only seen in the influence of physical parameters, such as ensuring protein stability and tertiary structure, providing the basis for rigid conformations and slowing down proteolytic degradation of the peptide chain; most of specialised recognition events have been allocated to N-glycans It is Molecules 2015, 20 clear that different types of O-glycans are relevant for many more functions, such as modulating of enzyme activity (e.g., the reversible attachment of an O-linked GlcNAc (N-acetylglucosamine) residue to cytoplasmic and nuclear proteins), modulating pro-protein processing and acting as signal molecules or sorting determinants guiding the modified protein in the cell from the place of biosynthesis to its target location [1,2,3,4]. O-GlcNAc see [16], for O-Fuc see [17], for O-Glc see [18], for O-Man (mannose) see [19,20] and for xylosyltransferases initiating proteoglycans see [21])
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