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Chapter 26

Chapter 26. Protein Sorting. 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. Overview. Cytoplasmic proteins

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Chapter 26

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  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 Mature protein N Cleavage site Hydrophobic (10-15 aa)

  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

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