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. In eukaryotes, it occurs in the endoplasmic reticulum, Golgi apparatus and occasionally in the cytoplasm; in prokaryotes, it occurs in the cytoplasm.Several different sugars can be added to the serine or threonine, and they affect the protein in different ways by changing protein stability and regulating protein activity. O-glycans, which are the sugars added to the serine or threonine, have numerous functions throughout the body, including trafficking of cells in the immune system, allowing recognition of foreign material, controlling cell metabolism and providing cartilage and tendon flexibility.Because of the many functions they have, changes in O-glycosylation are important in many diseases including cancer, diabetes and Alzheimer's. O-glycosylation occurs in all domains of life, including eukaryotes, archaea and a number of pathogenic bacteria including Burkholderia cenocepacia,Neisseria gonorrhoeae and Acinetobacter baumannii.

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Wiki: O-linked glycosylation

    N-linked glycosylation, is the attachment of an oligosaccharide, a carbohydrate consisting of several sugar molecules, sometimes also referred to as glycan, to a nitrogen atom (the amide nitrogen of an asparagine (Asn) residue of a protein), in a process called N-glycosylation, studied in biochemistry. The resulting protein is called an N-linked glycan, or simply an N-glycan.

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Wiki: N-linked glycosylation

    Here we show that disruption of SPPL3 caused CD19 hyperglycosylation which impairs the binding of anti-CD19 antibodies and impairs CAR T cell activation, thus enabling resistance to CAR therapy. We identify that hyperglycosylation of an asparagine residue proximal to the CAR binding epitope is directly responsible for enabling resistance.

Reference
Pubmed: Heard A, Landmann JH, Hansen AR, Papadopolou A, Hsu YS, Selli ME, Warrington JM, Lattin J, Chang J, Ha H, Haug-Kroeper M, Doray B, Gill S, Ruella M, Hayer KE, Weitzman MD, Green AM, Fluhrer R, Singh N. Antigen glycosylation regulates efficacy of CAR T cells targeting CD19. Nat Commun. 2022 Jun 11;13(1):3367. doi: 10.1038/s41467-022-31035-7.

    Glycosylation is the reaction in which a carbohydrate (or 'glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not always in chemistry), glycosylation usually refers to an enzyme-catalysed reaction, whereas glycation (also 'non-enzymatic glycation' and 'non-enzymatic glycosylation') may refer to a non-enzymatic reaction.

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Wiki: Glycosylation

    There are different enzymes to remove the glycans from the proteins or remove some part of the sugar chain. ¦Á2-3,6,8,9-Neuraminidase (from Arthrobacter ureafaciens): cleaves all non-reducing terminal branched and unbranched sialic acids. ¦Â1,4-Galactosidase (from Streptococcus pneumoniae): releases only ¦Â1,4-linked, nonreducing terminal galactose from complex carbohydrates and glycoproteins. ¦Â-N-Acetylglucosaminidase (from Streptococcus pneumoniae): cleaves all non-reducing terminal ¦Â-linked N-acetylglucosamine residues from complex carbohydrates and glycoproteins. endo-¦Á-N-Acetylgalactosaminidase (O-glycosidase from Streptococcus pneumoniae): removes O-glycosylation. This enzyme cleaves serine- or threonine-linked unsubstituted Gal¦Â1,3GalNAc PNGase F: cleaves asparagine-linked oligosaccharides unless ¦Á1,3-core fucosylated.

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Wiki: Deglycosylation

    C-linked glycosylation is essential for the trafficking, folding and function of secretory and transmembrane proteins involved in cellular communication processes. The tryptophan C-mannosyltransferase (CMT) enzymes that install the modification attach a mannose to the first tryptophan of WxxW/C sequons in nascent polypeptide chains by an unknown mechanism.

Reference
Pubmed: Bloch JS, John A, Mao R, Mukherjee S, Boilevin J, Irobalieva RN, Darbre T, Scott NE, Reymond JL, Kossiakoff AA, Goddard-Borger ED, Locher KP. Structure, sequon recognition and mechanism of tryptophan C-mannosyltransferase. Nat Chem Biol. 2023 May;19(5):575-584. doi: 10.1038/s41589-022-01219-9.