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读文献,涨知识。今天学习了解人类蛋白质糖基化途径。
Fig.3 | Human glycosylation pathways and enzymes. 糖基化途径的全局视图,糖链的主要结构元素以及糖基转移酶和碳水化合物硫酸转移酶的指定(预测的)生物合成角色(指示的是这些酶的编码基因;请注意,目前尚未报道启动针对免疫球蛋白样、plexin、转录因子(IPT)结构域的新型O-甘露糖化的酶)(问号))。16种已知的糖基化途径被组织成主要的生物合成步骤,这些步骤对途径(起始和核心延伸)和非特异性的生物合成步骤(延长(elongation)和分支(branching),以及封端(capping))具有特异性。对于涉及同工酶的途径,列出了所有异构体(带破折号或实线)。不同蛋白质糖基化途径的背景颜色模仿起始单糖的颜色(脂质糖基化通路显示为灰色),并且这些颜色在这些途径特定的糖基化步骤中保持不变。虚线表示硫酸软骨素(chondroitin sulfate,CS)和硫酸皮肤素(dermatan sulfate,DS)或硫酸乙酰肝素(heparan sulfate,HS)在常见四糖连接体(common tetrasaccharide linker)上生物合成的替代途径。该种显示有助于作为一个综合系统(integrated system)去研究单个基因以及糖基化过程。请注意,此处图示了糖基化途径的主要结构变化特征,但并非旨在显示细胞中发现的所有结构排列(structural permutations)和变化(variations)(仅针对选定结构指示对应连接(linkages))。关于所显示的糖基化酶的转录调控及其与先天性疾病和全基因组关联研究特征的关系的信息,请参见蛋白质糖基化——简介 appFigs 1 and 2(注意,此处所示和之前使用的水平方向相比,以垂直方向呈现生物合成途径)。*由于双途径特异性(dual pathway-specificity)而在图中出现2次的转移酶。COLGALT, collagen O-Gal transferase; DPY19L, dpy-19 like C-Man transferase; EOGT, epidermal growth factor-domain specific O-GlcNAc transferase; ER, endoplasmic reticulum; GALNT, polypeptide GalNAc-transferase; GDP, guanidine diphosphate; Hyl, hydroxylysine; LacNAc, N-acetyllactosamine (Galβ1–4GlcNAc); LAcDiNAc, N,N′-Diacetyllactosamine (GalNAcβ1–4GlcNAc); LLO, lipid-linked oligosaccharide; NS, non-specific; OGT, O-GlcNAc transferase; OST, oligosaccharyltransferase; POFUT, protein O-fucosyltransferase; POGLUT, protein O-Glc transferase; POMT, protein O-Man transferase; QC, quality control; R, variable underlying core glycan; S, sulfation; TMTC, transmembrane O-Man transferase targeting cadherins (also transmembrane and tetra-trico-peptide repeat (TPR) repeat-containing protein); XYLT, protein O-Xyl transferase.
Oligosaccharyltransferase (OST) complex 寡糖基转移酶(OST)复合物
A membrane protein complex in the endoplasmic reticulum that transfers an oligosaccharide from a dolichol pyrophosphate-activated donor to N-linked acceptor sequences on secreted proteins.
Translocon 转运子
A protein complex that mediates translocation of newly synthesized polypeptides from the cytosol across the endoplasmic reticulum membrane.
Oxidoreductase 氧化还原酶
An enzyme that catalyses thioldisulphide exchange reactions. In vivo oxidoreductases are important in the oxidative protein folding that takes place in the endoplasmic reticulum. Well-known examples are PDI and eRp57.
Lectin domains 凝集素结构域
Carbohydrate-binding protein domains.
Sulfation 硫酸化
An enzymatic process that transfers a sulfo group to another molecule, for example a glycan, by modifying a hydroxyl group on a monosaccharide by addition of a sulfo group. Sulfotransferases catalyse the reaction using 3′-phospho5′-adenylyl sulfate (PAPS) as a donor.
EGF-like repeats 表皮生长因子样重复序列
Common motifs of 30–40 amino acids found in the extracellular domain of transmembrane proteins or in proteins known to be secreted. The epidermal growth factor (EGF)-like repeats include six conserved cysteines forming three disulfide bonds.
Thrombospondin type 1 repeats(TSRs) 凝血酶敏感蛋白1型重复
Common protein motifs of 50–60 amino acids (6 conserved cysteines forming 3 disulfide bonds) found on transmembrane proteins and proteins in the extracellular matrix.
Mucin 粘蛋白
A large viscous heavily O-glycosylated protein. Mucins are the most abundant macromolecule in biofluids and mucus, covering most epithelial surfaces in the body.
α-Dystroglycan α-肌营养不良聚糖
Dystroglycan is encoded by the DAG1 gene and comprises two non-covalently-bound subunits (α and β). The extracellular α-subunit with the O-Man matriglycan provides binding to laminin, and the transmembrane β-subunit provides binding to dystrophin and the cytoskeleton.
Glycosaminoglycan chains (GAGs) 糖胺聚糖链
extended linear polysaccharides comprising repeating disaccharides.
Stoichiometry 化学计量
The fraction of a glycosylation site in a glycoprotein that is occupied by a glycan.
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