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Glycosidic bonds of the form discussed above are known as O-glycosidic bonds, in reference to the glycosidic oxygen that links the glycoside to the aglycone or reducing end sugar. In analogy, one also considers S-glycosidic bonds (which form thioglycosides ), where the oxygen of the glycosidic bond is replaced with a sulfur atom.
They are normally present as glycans: oligosaccharide chains are linked to lipids or to compatible amino acid side chains in proteins, by N- or O-glycosidic bonds. N-Linked oligosaccharides are always pentasaccharides attached to asparagine via a beta linkage to the amine nitrogen of the side chain. [7]
O-linked glycosylation is the attachment of a sugar molecule to the oxygen atom of serine (Ser) or threonine (Thr) residues in a protein. O-glycosylation is a post-translational modification that occurs after the protein has been synthesised.
Unlike the biochemical processes, synthetic glycochemistry relies heavily on protecting groups [18] (e.g. the 4,6-O-benzylidene) in order to achieve desired regioselectivity. The other challenge of chemical glycosylation is the stereoselectivity that each glycosidic linkage has two stereo-outcomes, α/β or cis/trans.
Glycosides can be linked by an O- (an O-glycoside), N- (a glycosylamine), S-(a thioglycoside), or C- (a C-glycoside) glycosidic bond. According to the IUPAC, the name "C-glycoside" is a misnomer; the preferred term is "C-glycosyl compound". [3] The given definition is the one used by IUPAC, which recommends the Haworth projection to correctly ...
The basic components are N-acetylglucosamine and N-acetyltalosaminuronic acid (bacterial peptidoglycan containing N-acetylmuramic acid instead), which are linked by β-1,3-glycosidic bonds. [3] Lysozyme, a host defense mechanism present in human secretions (e.g. saliva and tears) breaks β-1,4-glycosidic bonds to degrade peptidoglycan. However ...
The two most common linkages in glycoproteins are N-linked and O-linked glycoproteins. [3] An N-linked glycoprotein has glycan bonds to the nitrogen containing an asparagine amino acid within the protein sequence. [4] An O-linked glycoprotein has the sugar is bonded to an oxygen atom of a serine or threonine amino acid in the protein. [4]
O-GlcNAcylation is the process of adding a single N-acetylglucosamine sugar to the serine or threonine of a protein. [4] Comparable to phosphorylation, addition or removal of N-acetylglucosamine is a means of activating or deactivating enzymes or transcription factors. [4]