Cell Bio Part Deux

Cell Bio Part Deux - Ch 13 Intracellular vesicular traffic...

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Ch 13: Intracellular vesicular traffic Coated Vesicles - Cells segregate proteins into separate membrane domains by assembling a special protein coat on the membrane’s cytosolic face - Most transport vesicles form from specialized coated regions of membranes 2 functions of the coat proteins - To [] specific membrane proteins in a specialized patch which then gives rise to the vesicle membrane so that it selects the approp. Molecules for transport - Coat molds the forming vesicle, curved basketlike lattice that deforms the membrane and gives shape Three types of coated vesicles - Clathrin: mediate transport from the golgi and from the PM - COPI and COPII: transport from the ER and the Golgi cisternae The assembly of a clarhrin coat drives vesicle formation - COPII bud from the ER - COPI bud from golgi compartments - Clathrin subunits consists of 3 large and 3 small polypeptide chains that form 3 legged structure called triskelion o Assemble into a basketlike convex framework of hexagons and pentagons to form coated pits on the cytosolic surface of membranes - Adaptor proteins: form a discrete 2 nd layer of the coat. o binds clathrin coat to the membrane and traps various TMP including TMreceptors that capture soluble cargo molecules inside the vesicle o lateral interactions b/w adaptor complexes and b/w clathrin molecules aid in forming the vesicle Not all coats form basketlike structures - some are specialized protein assembles that form patches dedicated to specific cargo proteins - Retromer: assembles on endosomes and forms vesicles that return acid hydrolase receptors such as mannose 6 phosphate receptors to the Golgi o Multiprotein complex that assembles into a coat on endosomal membranes only when: It can bind to the cytoplasmic tails of the cargo receptors Can interact directly with a curved phosoplipid bilayer It can bind to a specific phosphorylated PIP, PIPs mark organelles and membrane domains - Form specialized membrane domains - Bind to many proteins involved at different steps in vesicular transport - Phosphorylation/ Cytoplasmic proteins regulate the pinching off and uncoating of coated vesicles - As the clathrin coat bud grows, soluble cytoplasmic proteins such as dynamin assemble as a ring around the neck of each bud.
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o The PIP binding domain of dynamin tethers the protein to the membrane and a GTPase domain, which regulates the rate at which vesicles pinch off from the membrane o Dynamin recruits other proteins to the neck of the budding vesicle and help to bend the patch of membrane o In addition, HSp70 chaperone proteins function as an uncoating atpase using the Energy of ATP hydrolysis to peel off the coat Monomeric GTPases control coat assembly - GTP binding proteins act as molecular switches which flip b/w ative and inactive - GEFs activate the proteins by catalyzing the exchange of GDP for GTP - GAPs inactivate proteins by exchanging GTP for GDp - Coat recruitments GTPases o ARF proteins: respon. For both COPI and Clathrin coast assembly @ golgi
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Cell Bio Part Deux - Ch 13 Intracellular vesicular traffic...

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