TABLE 9.
Protein glycosylation through different linkages and their function.
| Types | Linkages | Enzymes | Modified sequence in glycoproteins | Functions of glycosylation | |
|---|---|---|---|---|---|
| Sequence motifs | Specific domain | ||||
| N‐glycosylation | GlcNAc‐β‐Asn | OST complex (STT3A/STT3B) |
N‐X‐T/S, X≠P N‐G; N‐X‐C/V, X≠P |
None | Protein stability, 1118 protein folding and quality control, 1119 self/nonself recognition, 1120 cell adhesion 1121 , immunotherapy, 1122 receptor activation and endocytosis, 1123 glycoediting and drug delivery. 1124 |
| O‐glycosylation | GalNAc‐α‐Ser/Thr | GALNT1–20 | Weak isoform specific motifs 1093 | None | O‐glycan shielding is essential for secretion of an active protein, 1125 participates in immunological recognition of the immune system, 1082 protects membrane proteins from ectodomain shedding, 1090 increases the half‐life of peptide hormones in circulation, 1126 modulates the interaction between viral proteins and host surface receptors. 1127 O‐glycosylated mucins expressed at mucosal surfaces such as the respiratory and GI tract can form an effective barrier against pathogens. 1128 The particular glycosylation of LDLR class A repeat linker regions by GalNAc‐T11 alters the rate of uptake by cargo receptors. 1129 O‐glycan is also important for leukocyte extravasation. 1130 |
| GALNT11 | C6‐X3‐5‐T‐C1 1131 | LA | |||
| GlcNAc‐β‐Ser/Thr | EOGT | C5‐X2‐(G/P/S)‐(Y/F/W)‐(T/S)‐G‐X2‐C6 1132 | EGF | ||
| GlcNAc‐β‐Ser/Thr | OGT | None | None | ||
| Gal‐β‐Hyl | COLGALT1–2 | X‐Hyl‐Gly | Collagen repeats | ||
| Glc‐α‐Tyr | GYG | Tyr194 of GYG | None | ||
| Glc‐β‐Ser | POGLUT1 | C1‐X‐S‐X‐(A/P)‐C2 | EGF | ||
| POGLUT2–3 | C3‐X‐N‐T‐X‐G‐S‐(F/Y)‐X‐C4 | ||||
| Fuc‐α‐Ser/Thr | POFUT1 | C2‐X‐X‐X‐X‐(S/T)‐C3 | EGF | ||
| POFUT2 | C‐X‐X‐(S/T)‐C‐X‐X‐G | TSR | |||
| Man‐α‐Ser/Thr | POMT1–2 | None | None | ||
| TMTC1–4 | None | EC | |||
| Unknown | None | IPT | |||
| Xyl‐β‐Ser | XYLT1–2 | a‐a‐a‐a‐G‐S‐G‐a‐(a/G)‐a (“a” represents Asp or Glu) | None | ||
| C‐mannosylation | Man‐α‐Trp | DPY19L1–4 | W‐X‐X‐W | TSR | Support folding, enhance stability of thrombospondin repeats, 1106 regulate protein folding and maturation, 1133 play a key role in the folding, sorting and secretion of substrate proteins. 1107 , 1108 |
| Glypiation | Pr‐C(O)EthN‐6‐P‐Man | Transamidase | Carboxy‐terminal hydrophic segment | None | Regulate protein location on cell membrane, 1116 cell signal transduction, cell adhesion, and immune recognition. 1117 |