案例细胞生物学3secretion

1、CHAPTER 14Vesicular Traffic, Secretion, and EndocytosisOverview of major protein-sorting pathways in eukaryotesVesicle-based traffickingSignal based targeting Overview of the secretory and endocytic pathways of protein sorting.14.1 Molecular Mechanisms of Vesicle Budding and Fusion Assembly of a Pro

2、tein Coat Drives Vesicle Formation and Selection of Cargo MoleculesVesicle Formation Protein Coat v-SNARE Cargo protein t-SNARE GTPaseThe three different types of coated vesicles. Different coat proteins select different cargo and shape the transport vesicles that mediate the various steps in the bi

3、osynthetic-secretory and endocytic pathways.All are shown in electron micrographs at the same scale. (A) Clathrin-coated vesicles. (B) Golgi cisternae from a cell-free system in which COPI-coated vesicles bud in the test tube. (C) COPII-coated vesicles. Note that the vesicles with clathrin coats hav

4、e a more regular structure. Electron micrograph of clathrin-coated, COPI- coated, and COPII-coated vesiclesCOP:Cytosolic coat protein A Conserved Set of GTPase Switch Proteins Controls Assemblyof Different Vesicle CoatsARF proteins: COPI coat and clathrin coat assembly at Golgi membranes Sar1 protei

5、n: COPII coat assembly at the ER membrane The GTPase SwitchGuanine-nucleotide-exchange factors (GEFs) activate the proteins by catalyzing the exchange of GDP for GTP GTPase-activating proteins (GAPs) inactivate the proteins by triggering the hydrolysis of the bound GTP to GDP By binding to the COPII

6、 coat, membrane and cargo proteins e concentrated in the transport vesicles as they leave the ER. Membrane proteins are packaged into budding transport vesicles through the interactions of exit signals on their cytosolic tails with the COPII coat. Some of the membrane proteins trapped by the coat in

7、 turn function as cargo receptors, binding soluble proteins in the lumen and helping to package them into vesicles. A typical 50-nm transport vesicle contains about 200 membrane proteins, which can be of many different types. As indicated, unfolded or pletely assembled proteins are bound to chaperon

8、es and are thereby retained in the ER compartment. Targeting Sequence on Cargo Proteins Make Specific Molecular Contacts with Coat Proteins Rab GTPases Control Docking of Vesicles on Target MembraneV-SNAREt-SNARE Paired Sets of SNARE Proteins Mediate Fusion of Vesicles with Target MembraneAt least 2

9、0 different SNAREs in an animal cell Dissociation of SNARE pairs by NSF after a membrane fusion cycle is completed. After the v-SNAREs and t-SNAREs have mediated the fusion of a vesicle on a target membrane, the NSF binds to the SNARE complex via adaptor proteins and hydrolyzes ATP to pry the SNAREs

10、 apart NSF(N-ethylmaleimide-sensitive factor ): Protein with ATPase activity that disassembles a complex of a v-SNARE and a t-SNARE SNAREs: Soluble NSF Attachment protein REceptors Dissociation of SNARE Complexes After Membrane Fusion Is Driven by ATP Hy drolysis14.3 Early Stages of the Secretory Pa

11、thwayCOPII Vesicle Mediate Transport from the ER to the Golgi Sec23/sec24,Sec13 /Sec31, Sec16COPII coat proteinsCytosolic segments of ER membrane proteins contain diacidic sorting signal-DXECOP I Vesicle Mediate Retrograde Transport Within the GolgiAnd from the Golgi to the ER Recycle v-SNARE ER res

12、ident signal- KDEL sequence at C-terminus KDEL receptor (KKXX sequence at the very end of C-terminus) binds more tightly to their ligand at low pH. COP I coat proteins CoatmersSeven subunits The structure and functions of Golgi complexA.The polarity of Golgi complexCGN: Cis-Golgi-network TGN: Trans-

13、Golgi network Each Golgi stack has two distinct faces: a cis face (or entry face) and a trans face (or exit face). The Golgi apparatus. (A) Three-dimensional reconstruction from electron micrographs of the Golgi apparatus in a secretory animal cell. The cis-face of the Golgi stack is that closest to

14、 the ER. (B) A thin-section electron micrograph emphasizing the transitional zone between the ER and the Golgi apparatus in an animal cell. (C) An electron micrograph of a Golgi apparatus in a plant cell (the green alga Chlamydomonas) seen in cross section. In plant cells, the Golgi apparatus is gen

15、erally more distinct and more clearly separated from other intracellular membranes than in animal cells. Anterograde Transport Through the Golgi Occurs by Cisternal MaturationThe Golgi Cisternae Are Organized as a Series of Processing CompartmentsRetrograde transport vesicle14.4 Later Stages of the

16、Secretory Pathway Vesicles Coated with Clathrin and/or Adapter Proteins MediateTransport form the trans-Golgi Dynamin Is Required for Pinching Off of Clathrin VesiclesARF drives the pinch off of COPI vesicles from donor Membrane Hsc70 drives depolymerization of clathrin coat The structure and functi

17、ons of Lysosomes Characteristics of LysosomesLysosomes. The acid hydrolases are hydrolytic enzymes that are active under acidic conditions. The lumen is maintained at an acidic pH by an H+ ATPase in the membrane that pumps H+ into the lysosome. Histochemical visualization of lysosomes.Electron micro

18、-graphs of two sections of a cell stained to reveal the location of acid phosphatase, a marker enzyme for lysosomes. The larger membrane-bounded organelles, containing dense precipitates of lead phosphate, are lysosomes, whose diverse morphology reflects variations in the amount and nature of the ma

19、terial they are digesting. The precipitates are produced when tissue fixed with glutaraldehyde is incubated with a phosphatase substrate in the presence of lead ions. Two small vesicles thought to be carrying acid hydrolases from the Golgi apparatus are indicated by red arrows in the top panel. Lyso

20、somes Are HeterogeneousThe Functions of Lysosomes Lysosomes are involved in three major cell functions: phagocytosis; autophagy; endocytosis.Three pathways to degradation in lysosomes. (A) Each pathway leads to the intracellular digestion of materials derived from a different source. (B) An electron

21、 micrograph of an autophagosome containing a mitochondrion and a peroxisome. C. Lysosomes and DiseasesAutolysis: A break or leak in the membrane of lys releases digestive enzymes into the cell which damages the surrounding tissues (Silicosis).表1. 神经鞘脂贮积病疾病缺失酶类主要贮积底物后果GM1神经节苷脂贮积症GM1-半乳糖苷酶神经节苷脂GM1智力迟钝

22、，肝脏肥大，骨骼受累，2岁前死亡泰萨二氏病己糖胺酶A神经节苷脂GM2智力迟钝，失明，3岁前死亡法布莱氏病-半乳糖苷酶A三己糖神经酰胺皮疹，肾功能丧失，下肢疼痛山霍夫氏病己糖胺酶A和B神经节苷脂GM2和红细胞糖苷酯与泰萨氏疾病症状相似，但发展更快高歇氏病葡糖脑苷酯酶葡糖脑苷脂肝脏和脾脏肿大，长骨腐蚀，只在婴儿期发生智力迟钝尼-皮二氏病鞘磷脂水解酶鞘磷脂肝脏和脾脏肿大，智力迟钝Farbers 脂肪肉芽肿病神经酰胺水解酶神经酰胺疼痛性与退行性的关节变形，皮肤瘤，几年内死亡Krabbes 病半乳糖脑苷酯酶半乳糖脑苷脂髓磷脂缺失，智力迟钝，2岁前死亡脑硫脂沉积芳基硫酸酯酶脑硫脂智力迟钝，前十年死亡 Ly

23、sosomal storage diseases : the absence of one or more lysosomal enzymes, and resulting in accumulation of material in lysosomes as large inclusions Mannose 6-Phosphate (M6P) Residues Target Soluble Proteins to LysosomesFormation of mannose 6-phosphate(M6P) I-cell disease: enzymes are missing from th

24、e lysosomeEven in normal cells,some M6P receptors are secreted.Hepatocytes employ an M6P-independent pathway for for sorting lysosomal enzymes Figure 14.22 Trafficking of soluble lysosomal enzymes from the trans-Golgi network and cell surface to lysosomes.Protein Aggregation in the trans-Golgi May F

25、unction in Sorting Proteins to Regulated Secretory Vesicles.The constitutive and regulated secretory pathways Why ACTH,insulin,and trypsinogenSegregate into the same regulatedSecretory vesicles? Chromogranin A,chromogranin B and Secretogranin IIImports extracellular molecules dissolved or suspended

26、in fluid by forming vesicles from the plasma membranePhagocytosis (cellular eating) : involves the ingestion of large particles, such as microorganisms or dead cells via large vesicles called phagosomes (generally 250 nm in diameter). . Pinocytosis (cellular drinking): involves the ingestion of flui

27、d and solutes via small pinocytic vesicles (about 100 nm in diameter). Phagocytosis by a neutrophil. An electron micrograph of a neutrophil phagocytosing a bacterium, which is in the process of dividing. Specialized Phagocytic Cells Can Ingest Large ParticlesPhagocytosis by a macrophage. Ascanning e

28、lectron micrograph of a mouse macrophage phagocytosing two chemically altered red blood cells. The red arrows point to edges of thin processes (pseudopods) of the macrophage that are extending as collars to engulf the red cells. The formation of clathrin-coated vesicles from the plasma membrane.Thes

29、e electron micrographs illustrate the probable sequence of events in the formation of a clathrin-coated vesicle from a clathrin-coated pit. The clathrin-coated pits and vesicles shown are larger than those seen in normal-sized cells. They are involved in taking up lipoprotein particles into a very l

30、arge hen oocyte to form yolk. The lipoprotein particles bound to their membrane-bound receptors can be seen as a dense, fuzzy layer on the extracellular surface of the plasma membrane which is the inside surface of the vesicle. Cells Take Up Lipids from the Blood in the Form of Large,Well-Defined Li

31、poprotein ComplexesMost cholesterol is transported in the blood as cholesteryl esters in the form of lipid-protein particles known as low-density lipoproteins (LDL) Receptors for Low-Density Lipoprotein and Other Ligands Contain Sorting Signals That Target Them for EndocytosisNPXY sorting signalRece

32、ptors for Low-Density Lipoprotein and Other Ligands Contain Sorting Signals That Target Them for EndocytosisNPXY sorting signalSeven cysteine repeats The Acidic pH of Late Endosomes Causes Most Receptor-Ligand Complexes to Dissociate14.6 Directing Membrane Proteins and Cytosolic Materials to the Lysosome Multivesicular Endosomes Segregate Membrane