1. Previously Bio308 Hypotheses for molecular basis of bipolar disorder Suggest problem lies in protein targeting How are proteins targeted and delivered? Sorting places proteins in membrane and in lumen of organelles PM (and other) proteins use Sec or SRP mediated translocation to become inserted into the ER (and only the ER) After insertion non-ER proteins are sorted and delivered sorting lumenal vs membrane proteins –how? http://www.udel.edu/Biology/Wags/histopage/empage/ebv/ebv10.gif

2. Stages of vesicle traffic 3 Stages: Budding, targeting/docking and fusion Donor Target

3. Consequences of unregulated vesicular traffic Mixing of organelle contents (  won’t function correctly) Mislocalization of proteins (  won’t function correctly) Inappropriate levels of secretion (too hi or too lo) A Dead Cell

4. Vesicular traffic control How does a vesicle ‘know’ what components it should contain? How does it ‘know’ which membrane it should go to? How does it fuse when it gets there? Our neurotransmitter receptor need to go ‘through’ 5 cellular compartments before it gets to the post synaptic membrane

5. Content selection What goes inside which vesicle? Lumenal protein: Transmembrane proteins: Combination of cytosolic and lumenal proteins determine specific vesicle content

6. Budding Fig 17-58 CBI 13.1 Clathrin

7. Coat Components http://userpage.chemie.fu-berlin.de/biochemie/aghaucke/clath.jpg Clathrin COPI COPII Identity determined by what the vesicle contains and it’s coat.

8. Budding II ER vesicle budding Drin, G, and B. Antonny (2005) News and Views: Helices sculpt membrane. Nature vol: 437 Amino Acid Key Highly hydrophobic + charged - charged Other Hydroxylated Sar1p N-terminal helix Sar1p-GTP form exposes helix that anchors protein to ER surface by ‘floating’ with hydrophobic a.a. interacting with membrane core

9. Budding III Drin, G, and B. Antonny (2005) News and Views: Helices sculpt membrane. Nature vol: 437 ER vesicle budding Floating many Sar1p in top leaflet makes it ‘bigger’ than the bottom one. Results --> bulge that can more easily interact with coat proteins.

10. Fission ER vesicle budding….fission Ring of parallel helices at neck might aid fission. New data for ER; had seen a protein (epsin) help deform PM for clathrin coated vesicles. May suggest that using a helix to deform membrane is common mechanism for budding/fission

11. Targeting/Docking: http://dir2.nichd.nih.gov/nichd/cbmb/sob/in_vivo_dyn.html What happens after budding? How do vesicles dock with specific target membrane?

12. The SNARE hypothesis Fig 17-59 V-SNARE T-SNARE Role of p115 Role of Rab proteins retrograde

13. Synaptic vesicle fusion VAMP Syntaxin SNAP 25 Synaptotagmin Rab3a

14. Next: Moving in the other direction: endocytosis Types: Phagocytosis– specialized cells Pinocytosis– all cells Connection– perhaps the # of our receptor’s on PM is controlled by endocytosis Pinocytosis ‘problem’ rate of pinocytosis internalizes 100% of PM per hour ? (How can this be?)