Chapter 13 • Intracellular Vesicular Traffic 張學偉 助理教授
The molecular mechanisms of membrane transport and the maintenance of compartmental diversity
GFP-FUSION PROTEINS HAVE REVOLUTIONIZED THE STUDY OF INTRACELLULAR TRANSPORT
There are various types of coated vesicles Mediate transport from Golgi & from plasma membrane Mediate transport from ER & Golgi Each type is used for different transport steps in the cell.
The assembly of a clathrin coat drives vesicle formation
by charperone (hsp70) Major coat protein: clathrin & adaptin There are at least four types of adaptins, each specific for a different set of cargo receptor.
Both the pinching-off and uncoating of coated vesicles are regulated processes
Not all transport vesicles are spherical Various size & shape
Interacting SNAREs need to be pried apart before they can function again cytosol Cycle
Rab proteins (monomeric GTPase) help ensure the specificity of vesicle docking
Rab facilitate docking of transport vescicles. Rab &its effector Structure vary greatly Function common (1.concentrate & tether vesicle near target site 2. Trigger release of SNARP control protein) cycle
SNARE may mediate membrane fusion Process for SNARE concentrate in membrane fusion
ER exit site 50nm vesicle > 200 mem protein Cargo Recruitment
Only proteins that are properly folded and assembled can leave the ER Incomplete ER resident protein
CF (Cystic fibrosis) Defect in Cl- transport This is not because the mutation inactivated the protein, But because the active protein is discarded before it reaches the plasma membrane.
Transport from the ER to the Golgi apparatus is mediated by vesicular tubular clusters. Heterotypic fusion Homotypic memb fusion is not restricted to form VTC.
The structure formed when ER-derived vesicles fuse with one another are called.
The retrieval pathway to the ER uses sorting signals Lys-Asp-Glu-Leu (KDEL) Short retrieval signal at c-terminal Resident ER membrane protein KKXX at c-terminal end direct interact with COPI coat
Many proteins are selectively retained in the compartments in which they function Aggregation of proteins that function in the same compartment - called kin recognition
The golgi apparatus consists of an ordered series of compartments.
Two major classes of N-linked oligosaccharide complex High mannose No new sugar added in Golgi
High specific endoglycosidase Can distinguish between these two type
Proteoglycans are assembled in the Golgi Apparatus O-linked glycosylation Proteoglycans are secreted or anchored to plasma membrane
1. N-linked is prevalent in all eukaryotes, but absent in procaryotes. 2. limited flexibility. 3. Recognition 4. Regulation of development 5. Protective coat unit 6. Cell-cell adhesion What is the purpose of N-glycosylation?
The golgi cisternae are organized as a series of processing compartments