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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





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



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



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.




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



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




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