细胞生物学：Chapter 9. Endomembrane System or Intracellular compartment-3s

1、(胰岛素胰岛素) Proprotein processing in Golgi：inactive proprotein（GC）active polypeptide Protein transport through Golgi Protein Sorting and Protein Sorting and ExportExportER retention proteinslysosome proteins and membrane proteins Secretory proteins and extracellular matrix component-Sorting and Export

2、mainly depend on the interaction between signal sequence（or signal patch）of proteins sorted and . ER protein retention in ERER retention signal at their C-terminus: KDEL: Lys-Asp-Glu-Leu-COO-(e.g. Bip protein)KDEL signal -GC membrane): recognize the vesicles containing resident proteins and returnin

3、g the runaway proteins - ER membrane): receive the runaway proteinsSecretory pathwaysER ER lumen CGN Medial cisternae TGN plasma membrane (discharge) Cell secretion (Exocytosis：胞吐作用：胞吐作用)protein synthesisBuddingprocessingSorting and buddingfusion with plasma membranedischarge2021-7-106 Constitutive

4、secretion (exocytosis): vesicles continuously form and carry proteins from the Golgi to the cell surface. Regulated secretion (exocytosis) : hormones, mucus(黏液)or digestive enzymes are stored in secretory vesicles until an extracellular signal stimulates their secretion. 3）lysosome (溶酶体溶酶体)(1)(1)Mor

5、phologic StructureMorphologic StructureLysosomes: heterogenous vesicle-like organelles enclosed by a single layer of membrane contain many types of digestive enzymes. animal cells, diameter of 0.250.8m in varies in size, shape and electron density小鼠脾脏巨噬细胞中的溶酶体用电镜细胞化学技术显示其中含有的酸性磷酸酶，M：线粒体，L：溶酶体（朴英杰）核酸

6、酶核酸酶蛋白酶蛋白酶糖苷酶糖苷酶酯酶酯酶磷酸酶磷酸酶硫酸酶硫酸酶磷脂酶磷脂酶(2) Chemical composition approximately 50 different acid hydrolases in the lysosome lumen, their optimal activity at an acid pH 4.6 marker enzyme: acid phosphatase(酸性磷酸酶酸性磷酸酶) the proton pumps in the lysosome membranethe proton pump in the membraneacidic interna

7、l environmentFactors of lysosome membrane stability contains proton pumps (H+-ATPase) to maintain the high internal proton contains many types of transport proteins: export hydrolytic products of the digestion of macromolecules to the cytosol contains highly glycosylated membrane proteins: to form a

8、 protective layer preventing the membrane protein itself being degradated contains high level of cholesterol(3) Classification of lysosomesendosomesPhagocytosis异体吞噬异体吞噬Autophagy 自体吞噬吞噬初级溶酶体初级溶酶体初级溶酶体初级溶酶体次级溶酶体次级溶酶体次级溶酶体次级溶酶体Primary lysosome (初级溶酶体初级溶酶体): no visible granule or membrane fragments; aci

9、dic hydrolases short of activitySecondary lysosome (次级溶酶体次级溶酶体): acidic hydrolases and substrates（granule or membrane fragments). autolysosome (自噬性溶酶体自噬性溶酶体) heterolysosome (异噬性溶酶体异噬性溶酶体)residual body or post lysosome (残余小体或后溶酶残余小体或后溶酶体体)：no enzyme activity but indigested residue, such as age pigmen

10、t (epidermic cells) and lipofuscin-脂褐质脂褐质 (liver cells).12Endocytosis(胞吞作用)Endocytosis(胞吐作用胞吐作用) Endocytosis (胞吞作用) is a process by which eukaryotic cells take up fluid, large and small molecules as well. - Phagocytosis(吞噬作用吞噬作用), an actin-mediated process in which cells envelop bacteria and other l

11、arge particles in macrophage (巨噬细胞巨噬细胞) and neutrophils(中性粒细胞中性粒细胞).- Pinocytosis(胞饮作用胞饮作用), occurs continuously in almost all cellsmacrophageneutrophilspinocytosis14Receptor-mediated endocytosis LDL (low-density lipoproteins), transferrin (转铁蛋白：an iron-binding proteins), hormones (insulin) and glyc

12、oproteinsLDL: phospholipid and proteins-Cholesterol is from food or synthsized in the liver. -Transported in LDL-LDL receptor is synthesized when required, and incorported in plasma membrane.LDL(球形脂蛋白)核心核心800个磷脂分子个磷脂分子500个个辅基蛋白辅基蛋白B-100Binding to LDL receptorThe LDL receptor-mediated endocytosisLow

13、PH in the endosomes result in separation of LDL from its receptors.the estered cholesterol in LDL particles is hydrolyzed to release free cholesterollateearlyform clathrin-coated vesiclesLDL particles(4）Function of lysosomesPhagocytosis(吞噬作用吞噬作用)defense pathogen infection (heterolysosome) Autophagy(

14、自噬作用自噬作用) participate in intracellular digestion to provide nutrition for cells as intracelIular alimentary organs. degrade useless macromolecules, worn-out organelles and particles taken into the cell by endocytosis participate in secretion regulation：the lysosomes in glandular cells uptake secreto

15、ry granules with thyroid globulin and degradate the globulins into active thyroxin (甲甲状腺素状腺素). Autolysis (自溶作用自溶作用) participate in embryonic development and morphogenesis: degradation for tadpole tails. participating in fertilization海胆精子海胆精子消化卵细胞消化卵细胞外的物质外的物质存在于大多数动物精子头部顶端的细胞器 (5) Lysosome biogenesi

16、s溶酶体酶合溶酶体酶合成及糖基化成及糖基化修饰修饰寡糖链甘露糖寡糖链甘露糖残基磷酸化残基磷酸化溶酶体酶分选溶酶体酶分选磷酸基团被去除磷酸基团被去除-初级初级溶酶体溶酶体部分部分M6P受体也受体也会到达细胞质膜会到达细胞质膜M6P受体蛋白在受体蛋白在pH6.57的条件下与的条件下与M6P结合，在结合，在pH=6条件下脱落条件下脱落Mannose-6-phosphate（M6P） pathway endosomesM6P酶酶的识别的识别和分选和分选缺损途径（缺损途径（default pathway）受体介导受体介导在粗面内质网在粗面内质网合成后通过糖合成后通过糖基化和磷酸化基化和磷酸化添加标记添加

17、标记标记标记 6-磷酸甘露糖磷酸甘露糖(mannose 6-phosphate, M6P)。低低pH时时N-乙酰葡萄糖胺磷酸转移酶乙酰葡萄糖胺磷酸转移酶 (GlcNAc phosphotransferase) N-乙酰葡萄糖苷酶乙酰葡萄糖苷酶N-乙乙酰葡酰葡萄糖萄糖胺胺催化磷酸转移催化磷酸转移 PLANT CELL VACUOLES2.Characteristics of endomembrane systemIndependent e n c l o s e d compartments specialized function D y n a m i c a n d Interdepend

18、entBiosynthetic pathway Secretory pathway Endocytosis pathway:Vesicular transport-transport way of proteins and lipids*a dynamic, interconnected network：protein sortingProtein sorting inside cell Vesicular transport(小泡运输小泡运输)Proteins located in different compartments were sorted in different vesicle

19、s ？Known Sorting Signals That Direct Proteins to Specific Transport VesiclesSignal Sequence* Proteins with Signal Signal Receptor Vesicles Lys-Asp-Glu-Leu ER-resident luminal proteins KDEL receptor in COPI (KDEL) cis-Golgi membrane Lys-Lys-X-X ER-resident membrane COPI _and _subunits COPI (KKXX) pro

20、teins (cytosolic domain) Di-acidic Cargo membrane proteins in COPII Sec24 subunit COPII (e.g., Asp-X-Glu) ER (cytosolic domain) Mannose 6-phosphate Soluble lysosomal enzymes M6P receptor in trans-Clathrin/AP1 (M6P) after processing in cis-Golgi Golgi membrane Secreted lysosomal enzymes M6P receptor

21、in plasma Clathrin/AP2 membrane Asn-Pro-X-Tyr LDL receptor in the plasma AP2 complex Clathrin/AP2 (NPXY) membrane (cytosolic domain) Tyr-X-X- _ Membrane proteins in trans-AP1 (_1 subunit) Clathrin/AP1 (YXX_) Golgi (cytosolic domain) Plasma membrane proteins AP2 (_2 subunit) Clathrin/AP2 (cytosolic d

22、omain) Leu-Leu Plasma membrane proteins AP2 complexes Clathrin/AP2 (LL) (cytosolic domain) *X, any amino acid; _hydrophobic amino acid. Single-letter amino acid abbreviations are in parentheses.(1）Types of coated vesicles（衣被小泡）衣被小泡）clathrin-coated vesicle (网格网格蛋白有被小泡蛋白有被小泡)COPII-coated vesicles (COP

23、II有被有被小泡小泡)COPI-coated vesicles (COPI有被有被小泡小泡)(2)Transport routes of coated vesicles in cellsERGolgiLysosomePlasma membraneCOPIIClathrinClathrinplant vacuoleCOPIendosomeCGN TGNCOPIClathrinClathrinClathrin27（3）Formation of coated vesicles clathrin coated vesicles 三个三个Clathrin二聚二聚体体三脚蛋白复合三脚蛋白复合体（体（tri

24、skelion）Clathrin coated pits28(coat-recruitment GTPase)Coat formation衔接蛋白识别受体衔接蛋白识别受体（发动蛋白）（发动蛋白）发动蛋白也是网格小泡形成的装配反应因子发动蛋白也是网格小泡形成的装配反应因子COPI-coated vesicles: -装配反应因子：一种装配反应因子：一种单体单体GTPase）与）与GTP结合，结合，构型改变，脂肪酸链暴露，插构型改变，脂肪酸链暴露，插入供体膜中，同外被体结合，入供体膜中，同外被体结合，形成被膜小泡。形成被膜小泡。 -COPI（similar to clathrin）：）：在出芽小泡

25、的胞质溶胶面聚合，在出芽小泡的胞质溶胶面聚合，形成形成COPI被膜小泡被膜小泡COPII-coated vesicles （最早发现-酵母）Sar1(coat-recruitment GTPase)Coat formation的鸟的鸟苷酸交换苷酸交换因子因子大多数跨膜蛋白是直接结合在大多数跨膜蛋白是直接结合在COP II衣被上，少数跨衣被上，少数跨膜蛋白和多数可溶性蛋白通过受体与膜蛋白和多数可溶性蛋白通过受体与COP II衣被结合衣被结合3.Biological significance of endomembrane systemsform some functionally specialized compartments -provide microenvironment