1. Chapter 26 Protein Sorting

2. Chapter Objectives Understand the pathways of cotranslational processing of proteins – ER, Golgi, Plasma membrane, Lysosomes Understand the pathways of posttranslational processing of proteins – Mitochondria, Peroxisomes, Nucleus

3. Overview Cytoplasmic proteins Mitochondria, peroxisome, or nuclear proteins Extracellular, lysosomal, ER proteins

4. Cell Reminder

5. ER

6. Golgi

7. How do proteins know where to go? Signal Peptide – Sends proteins to ER – No signal, to the cytosol Blobel 1999 Nobel Prize Some polar Hydrophobic (10-15 aa) Mature protein Cleavage site N

8. To the ER! GDP GTP GDP

9. Oligosaccharides – N-linked

10. Goodbye ER, Hello Golgi Must physically cross a space. COP-coated vesicles – Coat protein complex COP-II sends vesicles to Golgi

11. Finding a Target ARF GTPase activity activated at target – Coat is removed Target – Plasma membrane Nerve cells – Other organelles

12. Oops!! Goodbye Golgi, Hello ER COP-I KDEL sequence in protein

13. Review

14. To the Lysosome Vesicles bud from Golgi to a variety of places – Lysosomes Termernal glycosylation is mannose 6P Destructive

15. Clathrin-coat Another way to make vesicles – Dynamin pinches vesicle GTP dependent – Clathrin-coated vesicles become endosomes Endosomes can become or fuse with lysosomes.

16. Integral Membrane Proteins

17. To the Mitochondria

18. To the Peroxisome Peroxisomes are thought to be artifact organelles – Oxidation reactions Without producing energy – Break down lipids – No synthesis of proteins – PTS1 and PTS2 are signals to import proteins PTS1 has a c-terminal SKL tripeptide

19. To the Nucleus Transport proteins – Proteins and RNA are leaving the nucleus – Proteins are trying to get into the nucleus – Some proteins are really big Nuclear Pore Complex (nucleoporin) – Very big allows diffusion of up to 40,000 Da proteins – Larger proteins must be accepted by complex

20. Nuclear Pore Complex

21. Big Protein Transport NLS (nuclear localization signal) – Very positive charge PKKKRKV KRxxxxxxxxxxPAAIKKAGQAKKKK NES (nuclear export signal) Some proteins go both ways – Heteroribonucleoprotein complex (hnRNP) Shuttles mRNA out of nucleus Returns to pick up more 38 amino acid signal sends it both directions

22. Entropy and Transport to Nucleus Not energy mechanism innate to nucleoporin Uses small GTP/GDP binding protein Ran

23. Ran as an Energy Mechanism

24. Controlling Export/Import