Cell Bio: Chapter 10 Protein Trafficking through the cytosol

Signal sequence

• written into AA sequence

• Usually on N terminus

• Driven by hydrophobicity and amino acid composition

Why are signal sequences necessary?

Without signal sequence protein can not get final destination

Why are signal sequences sufficient?

Nothing else but signal sequence is required to get proteins to their final destination

Nuclear Pore Complexes

• entrance and exit of nucleus

• Enormous stucture

• Allows movement of proteins, mRNAs and rRNA

Cytosolic side of NPC

• cytoplasmic filaments

Cytoplasmic filaments

• docking stations for the NPC

Central Channel of NPC

• surrounded by central ring

• Cytoplasmic ring

• Spoke ring

• Nucleoplasmic ring

Cytoplasmic ring

Top ring of the NPC central channel

Spoke ring

Middle ring of the NPC central channel

Nucleoplasmic ring

Bottom ring of the NPC central channel

Nucleoplasm side of the NPC

• nuclear basket

Nuclear Basket

• catches everything being transported into the nucleus

Nucleocytoplasmic transport through diffusion

• small molecules

• Ions

• Small proteins

Nucleoplasmic Transport through signal based transport

• med/large proteins or nucleic acids

• NLS

• NES

• Signal interacts with shuttle protein to cross NPC

NLS

• nuclear localization signal

• Short amino sequence that tags proteins for transport into the nucleus of a cell

NES

• Nuclear export signal

• Short segament of hydrophobic amino acids that facilitates the movement of proteins out of the nucleus

Nuclear Import

1. Cargo protein NLS bind to importin

2. Importing binds to cytoplasmic filaments

3. Importing/protein binds RAN-GTP

4. Releases cargo protein

Shuttle protein for movement into the NPC

Importin

Resetting NPC

1. RAN-GTP-importin crosses back to cytosol

2. GTP-ase activating protein binds to RAN and GTP hydrolyzed

3. Next import occur

4. GDP replaced by GTP so cycle can cotinue

Nuclear Export

1. Ran-GTP binds to cargo protein-exportin complex

2. In cytosol, GTP hydorlysis releases cargo protein

3. Ran-GTP diffuses back into nucleus

Endosymbiosis

• hypothesized evolvement of the mitochondria and the chloroplasts

How many membranes do the mitochondria have?

2

How many membranes do the chloroplasts have?

3

TOM

Translocase of outer mitochondrial membrane

Outer mitochondrial membrane proteins

• inserted into TOM and released into the membrane

Intermembrane space proteins of mitochondria

• pass through TOM

• In floating fluid between inner and outer membranes

Inner mitochondrial membrane proteins

• pass through TOM

• Inserted into TIM

• Released into membrane

TIM

Translocases of inner mitochondrial membrane

Mitochondrial matrix proteins

• pass through TOM and TIM

• Fold here

Chloroplasts Trafficking

• TOC and TIC

TOC

• takes proteins to intermembrane space

TIC

• takes proteins to stroma

Peroxisomes

• in all eukaryotic ells

• Function in detoxification and lipid metabolism

• Targeted by Pex5

Trafficking to peroxisomes

• use both pathways

Cytosolic pathway proteins to peroxisomes

• have peroxisome targeting signal (PTS)

• Translocated whole (no folding)

Endomembrane Pathway proteins to peroxisome

• ER to Golgi to vesicle to fusion to peroxisome