Chapter 26
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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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Chapter 26

Chapter 26

Protein Sorting


Chapter objectives

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

Overview

  • Cytoplasmic proteins

  • Mitochondria, peroxisome, or nuclear proteins

  • Extracellular, lysosomal, ER proteins


Cell reminder

Cell Reminder


Chapter 26

ER


Golgi

Golgi


How do proteins know where to go

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)


To the er

To the ER!

GDP

GTP

GDP


Oligosaccharides n linked

Oligosaccharides – N-linked


Goodbye er hello golgi

Goodbye ER, Hello Golgi

  • Must physically cross a space.

  • COP-coated vesicles

    • Coat protein complex

  • COP-II sends vesicles to Golgi


Finding a target

Finding a Target

  • ARF GTPase activity activated at target

    • Coat is removed

  • Target

    • Plasma membrane

      • Nerve cells

    • Other organelles


Oops goodbye golgi hello er

Oops!! Goodbye Golgi, Hello ER

  • COP-I

  • KDEL sequence in protein


Review

Review


To the lysosome

To the Lysosome

  • Vesicles bud from Golgi to a variety of places

    • Lysosomes

      • Termernal glycosylation is mannose 6P

      • Destructive


Clathrin coat

Clathrin-coat

  • Another way to make vesicles

    • Dynamin pinches vesicle

      • GTP dependent

    • Clathrin-coated vesicles become endosomes

      • Endosomes can become or fuse with lysosomes.


Integral membrane proteins

Integral Membrane Proteins


To the mitochondria

To the Mitochondria


To the peroxisome

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


To the nucleus

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


Nuclear pore complex

Nuclear Pore Complex


Big protein transport

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


Entropy and transport to nucleus

Entropy and Transport to Nucleus

  • Not energy mechanism innate to nucleoporin

  • Uses small GTP/GDP binding protein Ran


Ran as an energy mechanism

Ran as an Energy Mechanism


Controlling export import

Controlling Export/Import


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