Chapter 13: Intracellular Membrane Traffic

There are at least two layers to clathrin coated vesicles. Which proteins make up each layer and what is the overall function of each layer?
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There are at least two layers to clathrin coated vesicles. Which proteins make up each layer and what is the overall function of each layer?
Outer Layer: clathrin proteins- determines the geometry and structure of vesicles
Inner Layer: adaptor proteins - attach clathrin cage to the membrane by binding to cargo receptors - determines the content and cargo of vesicle.
Image: There are at least two layers to clathrin coated vesicles. Which proteins make up each layer and what is the overall function of each layer?
What is the role of phosphoinositides in vesicular trafficking?
- different phosphorylated versions are highly compartmentalized
- different proteins bind to different versions of PI's
- Specific adaptors bind to specific PI's
- binding of AP2 to PIP2 induces a conformational change that leads to complex formation
Image: What is the role of phosphoinositides in vesicular trafficking?
Describe the mechanism of dynamin's role in the pinching off of clathrin coated vesicles?
- dynamin binds to PIP2 in the membrane
- multiple dynamins form a spiral around the neck of a budding vesicle
- GTPase activity determines the rate of pinching off
- GTPase activity leads to a conformational change in dynamin that leads to constriction of the membrane neck
Image: Describe the mechanism of dynamin's role in the pinching off of clathrin coated vesicles?
Describe the mechanism shown in figure 13-16.
- Rab-GTP binds to a filamentous tethering protein
- leads to change in confirmation of tethering protein
- brings V-SNARE into contact with t-SNAREs
- Rab-GAP turns off Rab, releasing it from the membrane
- Rab-GDP is kept inactive in the cytosol through interaction with GDI
Image: Describe the mechanism shown in figure 13-16.
Describe the positive feedback mechanism for the pathway shown in figure 13-17.
- Rab5 GEF activates Rab 5, which leads to insertion into endosome membrane
- Active Rab5 recruits more Rab5
- Rab5 activates PI3-kinase, increasing PI3P
-PI3P and Rab5 recruit more Rab5 and tethering proteins forming a Rab5 membrane domain
- Rab5 also recruits more Rab5-GEF
Image: Describe the positive feedback mechanism for the pathway shown in figure 13-17.
Describe the mechanism by which SNARE proteins facilitate vesicle fusion. (see figure 13-19).
- binding of v-SNARE to t-SNARE leads to helical domains wrapping around one another
- forms 4-helix bundle termed a tran-SNARE complex
-Ratcheting of helical domains of v-and t-SNARES removes water from between the membranes
- contact between the two cytosolic leaflets of the membranes forms a stalk and exchange of phospholipids
- membrane fused
Image: Describe the mechanism by which SNARE proteins facilitate vesicle fusion. (see figure 13-19).
What is the function of NSF?
- hexameric ATPase enzyme
- uses the energy from ATP hydrolysis to unravel the helical domains of v- and t-SNARES
Image: What is the function of NSF?
What is a KDEL sequence?
- Signal sequence for resident ER proteins - KDEL receptors capture cargo proteins that contain the KDEL sequence
- lower pH in the Golgi may increase affinity of KDEL receptor for KDEL sequence
- higher pH in ER leads to release of KDEL from receptor
Image: What is a KDEL sequence?
Describe the mechanisms of synaptic vesicles priming and release shown in figure 13-67.
- Priming: synaptobrevin (v) and syntaxin (t) and SNAP-25 (t) partially interact forming a preliminary trans-SNARE complex. Complexin binding prevents further formation of SNARE bundling.
- Fusion: Ca2+ increase binds to synaptotagmin, which finishes the formation of the complex and initiates fusion.
Image: Describe the mechanisms of synaptic vesicles priming and release shown in figure 13-67.
What is the take home from figure 13-69?
very crowded environment.
Image: What is the take home from figure 13-69?