INTD5000, Lectures C7 & C8 Professor Eileen M. Lafer Tel#: 7-3764 Email: [email protected]
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Transcript of INTD5000, Lectures C7 & C8 Professor Eileen M. Lafer Tel#: 7-3764 Email: [email protected]
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INTD5000, Lectures C7 & C8Professor Eileen M. Lafer
Tel#: 7-3764
Email: [email protected]
Office: Room 415B
THE SECRETORY AND ENDOCYTIC PATHWAYS
Reading: Chapters 12 and 13 from Alberts et al.,
Molecular Biology of the Cell
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CELL COMPARTMENTS(ANIMATION 12.1 ALBERTS)
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THREE TYPES OF PROTEIN MOVEMENT BETWEEN COMPARTMENTS
Gated transport: nuclear pore complex, cytosol<-> nucleus
Transmembrane transport: protein translocators (proteins usually unfold), cytosol-> ER,
cytosol-> mitochondria
Vesicular transport: membrane-enclosed transport, ER <-> golgi
post-golgi traffic Alberts
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THE BIOSYNTHETIC-SECRETORY ANDENDOCYTIC PATHWAYS
Alberts
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ENDOPLASMIC RETICULUM (ER):
An extensive tubovesicular network where proteins and lipids are made.
Rough ER: studded with ribosomes, site of protein biosynthesis
Smooth ER: site of lipid biosynthesis
Alberts
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ROUGH ER
Alberts
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SMOOTH ER
Alberts
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Alberts
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PROTEIN SYNTHESIS AND TRANSLOCATION IN THE ROUGH ER
Animation 12.6, Alberts
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PROTEIN GLYCOSYLATION IN THE ROUGH ER: During translation, a signal sequence on membrane and secretory proteins directs the nascent protein into the ER lumen. After the protein has entered the ER, the glycosylation process begins.
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A PRE-FORMED PRECURSOR
OLIGOSACCHARIDE IS TRANSFERRED
EN BLOC TO PROTEINS
IN THE ER
Alberts
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PROTEIN GLYCOSYLATION IN THE ROUGH ER
Alberts
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SOME PERIPHERAL MEMBRANE PROTEINS AQUIRE A COVALENTLY ATTACHED
GLYCOPHOSPHATIDYLINOSITOL (GPI) ANCHOR IN THE ER
Alberts
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THE BIO-SYNTHETIC SECRETORY AND ENDOCYTIC PATHWAYS
Alberts
Retrieval pathways are in blue.
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MOVIE: MOVEMENT OF A FLUORESCENTLY TAGGEDMEMBRANE PROTEIN THROUGH THE SECRETORY PATHWAY
Alberts Video 13.2
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EXOCYTOSIS AND ENDOCTYOSIS
Alberts
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VESICULAR TRANSPORT
Alberts
Transport vesicles bud from one compartment and fuse with another, carrying material from the lumen of the donor compartment, and depositing it in the lumen of the target compartment.
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VESICULAR TRANSPORT IS MEDIATED BY COATED VESICLES
Alberts et al., Molecular Biology of the Cell-3rd edition
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THERE ARE VARIOUS TYPES OF COATED VESICLES
Alberts
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DIFFERENT COATS ARE USED IN DIFFERENT TRAFFICKING PATHWAYS
Alberts
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CLATHRIN-COATED VESICLES ARE THE MOST WELL CHARACTERIZED TRANSPORT VESICLES
John Heuser
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Ungewickell and Branton
THE STRUCTURE OF A CLATHRIN TRISKELION
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THE STRUCTURE OF A CLATHRIN COAT
Kirchhausen, Harrison, Walz, Fotin
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The Assembly and Disassembly of a Clathrin Coat
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Monomeric AP Family Tetrameric AP Family (also called adaptins)
Clathrin assembly
N C
AP180 AP-2
Clathrin assembly
AP180 Synaptic Plasma Membrane AP-1 TGNCALM Ubiquitous AP-2 Plasma Membrane
AP-3 Endosome/LysosomeAP-4 TGN
PIP bindingPIP binding
THE CLATHRIN ASSEMBLY PROTEINS
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Adaptins (AP-1, AP-2, AP-3, AP-4) Select Cargo For Inclusion Into Coated Vesicles, and Promote Clathrin
Polymerization
Alberts et al., Molecular Biology of the Cell
YXX
LL
NPXY-clathrin TD
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AP180 Promotes the Formation of Homogeneously Sized Vesicles
Clathrin Cages Assembled in vitro Without AP180
Clathrin Cages Assembled In vitro With AP180
Synaptic Vesicles in DrosophilaLacking Fly AP180 Gene lap
Synaptic Vesicles in Wild Type DrosophilaContaining Fly AP180 Gene lap
Ye & Lafer, 1995 Zhang, Koh, Beckstead, Budnick, Ganetzky, & Bellen, 1998
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AP180 recruits clathrin to the membrane via interactions with the phosphoinositide PIP2, and stimulates coat formation.
Matthew Higgins and Harvey McMahon
Diameter of lattice: 66nm
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THE GTPase DYNAMIN PROMOTES MEMBRANE SCISSION
Alberts
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How do clathrin coated vesicles uncoat?
clathrinAPs
Ca++
auxilinHsc70
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How do clathrin coated vesicles uncoat?
clathrinAPs
Ca++
Auxilin-HPDHsc70
Disrupt Interaction Between Hsc70 and Auxilin
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Auxilin HPD Increases the Numberof Coated Vesicles by 6 Fold:
0
1
2
HPDAuxilin Control
#CV
s / A
Z
Auxilin
** **
Auxilin HPD
J.R. Morgan, K. Prasad, S. Jin, G.J. Augustine, and E.M. Lafer. Uncoating of Clathrin-Coated Vesicles in Presynaptic Terminals: Roles for Hsc70 and Auxilin.
Neuron 32: 289-300 (2001).
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Auxilin Recruits and Activates the Uncoating ATPase Hsc70 to Clathrin Coated Vesicles
clathrinAPs
Ca++
auxilinHsc70
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The Clathrin Coated Vesicle Cycle
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CLATHRIN – THE MOVIEANIMATION 13.1 ALBERTS
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ASSEMBLY AND BUDDING OF COPII and COPI COATED VESICLES
FROM: Lee et al., Annu. Rev. Cell Dev. Biol. 20:87-123, 2004.
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STRUCTURE OF THE SEC13/31 COPII COAT
FROM: Stegg et al., Nature 439: 234-239, 2006.
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MOVIE: STRUCTURE OF THE SEC13/31 COPII COAT
FROM: Stegg et al., Nature 439: 234-239, 2006.
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ORIENTATION OF THE SEC13/32 HETEROTETRAMER IN THE SELF-ASSEMBLED OCTAHEDRAL CAGE
FROM: Stegg et al., Nature 439: 234-239, 2006.
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SNARE PROTEINS CONTRIBUTE TO THE SELECTIVITY OF VESICLE-TARGET DOCKING AS WELL AS TO THE FUSION PROCESS
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SNARE PROTEINS:
The group of proteins commonly referred to as SNARES forSoluble NSF Attachment REceptorS
were originally discovered as the synaptic proteins:VAMP/synaptobrevin
syntaxinSNAP-25
They were later re-discovered as the receptors for the soluble Golgi trafficking protein SNAP – Soluble NSF Attachment Protein.
NSF (NEM-Sensitive Fusion factor)
The SNARE proteins were also identified as substrates for the clostridial neurotoxins, potent agents which inhibit
neurotransmitter release.
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The SNARE Complex:
The synaptic vesicle membrane protein synaptobrevin (v-snare), forms a tight ternary complex with the presynaptic plasma membrane proteins syntaxin (t-snare), and SNAP-25 (t-snare). The stoichiometry of the proteins in the complex is 1:1:1 and it is resistant to SDS. This complex can be actively disassembled by the ATPase NSF, together with -SNAP.
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FROM: Sutton et al., Nature 395: 347-353, 1998.
Topology and organization of the synaptic fusion complex. a, Backbone ribbon drawing of the synaptic fusion complex: blue, synaptobrevin-II; red, syntaxin-1A; green, SNAP-25B (Sn1 and Sn2).
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Hypothetical model of the synaptic fusion complex as it joins two membranes, and location of neurotoxin-mediated cleavage sites. We extended the synaptic fusion complex crystal structure to include the transmembrane domains (yellow) of syntaxin-1A (red) and synaptobrevin-II (blue), and the loop connecting the Sn1 and Sn2 fragments (green). The transmembrane domains and the linker to the Sx fragment are represented as -helices. Hypothetical bends of the syntaxin and synaptobrevin -helices were modelled close to the lipid bilayers. The loop between the Sn1 and Sn2 fragments was modelled as an unstructured polypeptide chain. The conformation of this loop is speculative. The loop between the Sn1 and Sn2 domains is shown in orange.
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A MODEL FOR HOW
SNARE PROTEINS
MAY CATLYZE
MEMBRANE FUSION
Alberts
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DISSOCIATION OF SNARE PAIRS BY NSF FOLLOWING A CYCLE OF MEMBRANE FUSION
Alberts
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RAB PROTEINS ARE SMALL GTPases THAT GUIDE VESICLE TARGETING
Alberts
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Alberts
TRANSPORT FROM THE ER THROUGH THE GOLGI APPARATUS
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PROTEINS LEAVE THE ER IN COPII-COATED TRANSPORT VESICLES
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ER RESIDENT PROTEINS
CONTAIN A KDEL SEQUENCE THAT INTERACTS WITH THE COPI COAT AND PERMITS
THEIR RETRIVALFROM THE GOLGI BACK TO THE ER
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A MODEL FOR THE RETRIEVAL OF SOLUBLE ER RESIDENT PROTEINS
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THE GOLGI APPARATUS CONSISTS OF AN ORDERED SERIES OF COMPARTMENTS
Alberts
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THE TRANSITIONAL ZONE BETWEEN THE ER AND GOLGI
Alberts
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THE GOLGI APPARATUS
Alberts
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OLIGOSACCHARIDE CHAINS ARE PROCESSED IN THE GOLGI APPARATUS
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TRANSPORT INTO THE CELL FROM THE PLASMA MEMBRANE: ENDOCYTOSIS
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PINOCYTIC VESICLES FORM FROM COATED PITS IN THE PLASMA MEMBRANE
1. The major type of endocytic vesicles are the clathrin coated vesicles (CCVs).
The CCVs shown below are from a hen oocyte taking up lipoprotein particles to form yolk:
Alberts
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2. Caveolae are a less well understood type of endocytic coated vesicle that are involved in the endocytosis of lipid rafts from the plamsa membrane. Their major structural proteins are caveolins which are integral membrane proteins. Alberts
Alberts
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ENDOCYTOSIS IS IMPORTANT FOR CELLS TO:
1.Import selected extracelluar molecules (i.e. receptor-mediated endocytosis).
2.Regulate levels of membrane proteins on the cell surface (i.e. receptor down-regulation).
3. Synaptic vesicle recycling and biogenesis.
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EXAMPLE: RECEPTOR MEDIATED ENDOCYTOSIS
Cholesterol molecules are
packaged in LDL particles.
Alberts
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RECEPTOR-MEDIATED ENDOCYTOSIS: THE MOVIEAnimation 13.3 from Alberts
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EXOCYTOSIS
Alberts
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SECRETORY VESICLES BUD FROM THE TRANS-GOLGI
Alberts
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EXOCYTOSIS OF
SECRETORY VESICLES
The release of insulin from a
secretory vesicle of a pancreatic
beta cell.
Alberts
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SYNAPTIC TRANSMISSION IS AN EXAMPLE
OF REGULATEDEXOCYTOSIS
SYNAPTIC
TRANSMISSION IS ALSO AN
EXAMPLE OF A COUPLED
EXO-ENDOCYTIC
CYCLEAugustine