Protein Trafficking Flashcards
What are the three domains of the endoplasmic reticulum and their functions?
Smooth ER - lipid metabolsim
Rough ER - protein synthesis
ERGIC - vesicles exit to golgi
What are two destination pathways for proteins?
Cytosolic pathway
Secretory pathway
What are two ways proteins get into the ER?
Co-translational translocation
Post-translational translocation
What is the role of the signal recognition particle?
SRP binds the signal sequence, halting translation.
Also binds the SRP receptor on the RER
What is the function of the translocon?
To allow proteins to be translated into the ER and insert transmembrane portions into the membrane
What is the role of Hsp70 and Hsp40?
Maintains the protein in an unfolded state so that it can be transported to the ER.
What is the role of Sec62/63?
Recognizes the signal sequence of a completed polypeptide and causes translocon to open
What is the function of BiP?
Internal chaperone that acts as a molecular ratchet to drive translocation into the ER.
ATP-dependent
How does a transmembrane portion enter the membrane?
Exits the translocon laterally after it is translated.
Multiple domains mediated by SRP
What four protein processing mechanisms occur in the ER?
- BiP mediates folding
- Protein disulfide isomerase
- N-linked glycosylation
- GPI anchors
What are two types of export signals that trigger export from the ER to the golgi?
- Di-acidic or di-hydrophobic AA signals in the cytosolic domain
- GPI anchors
What is the ERES
Specialized region of the ER where proteins and phospholipids are exported.
How are proteins transported between the ER and golgi?
Proteins in the lumen of one organelle are packaged into budding transport vesicles, then released to the lumen of the recipient organelle
topology is maintained
What is the default pathway?
Pathway by which unmarked proteins in the ER can be packaged and transported to the golgi
What is the ERGIC?
ER-Golgi Intermediate complex
What is the role of the Golgi Apparatus?
- Process and sort proteins coming from ER
- Transport to endosomes, lysosomes, PM, or secretion
- most glycolipids and sphingomyelin are synthesized here
What are the four regions of the Golgi and their functions?
Cis - receives molecules from the ERGIC
Medial and trans - modifications
Trans-Golgi network - sorting and distribution
What occurs to N-linked oligosaccharides
- Mannoses are replaced with NAG, galactoses, and sialic acids
- Fucose is added to origin NAG
How are the N-linked oligosaccharides of lysosomal proteins modified?
Mannose phosphorylation
Recognized by a mannose-6-phosphate receptor in the trans Golgi Netowrk
What is O-linked Glycosylation?
Carbohydrate addition ot serine and threonine in the Golge
What happens to proteins that are destined to stay in the Golgi?
They are associated with the membrane and contain signals that prevent packaging and transport
What are the three routes that transport from the Golgi to the cell surface can occur?
- Direct transport
- Recycling endosomes
- Regulated secretory pathways
What is regulated release and what types of molecules are regulated this way?
Contents are stored in granules until signals direct their fusion with the PM
Hormones and neurotransmitters
What is the function of COPII-coated vesicles?
Carry proteins forward from the ER–>ERGIC–>Golgi
What is the function of COPI-coated vesicles?
Bud from ERGIC or Golgi and carry their cargo backwards to earlier compartments
What is the function of clatherin-coated vesicles?
transport in both directions between the trans Golgi network, endosomes, lysosomes, and PM
What is the KDEL sequence?
Tags ER-resident soluble proteins for return to the ER by COPI vesicles
What is the role of Mannose 6-phosphate?
Tags soluble lysosomal enzymes and secreted lysosomal enzymes for transport to lysosomes via Clatherin coated vesicles
What are ARF1 and Sar1?
Small GTP-binding proteins that regulate the formation of coated vesicles
How are clatherin-coated vesicles formed?
- GEF activates ARF1
- ARF binds an adaptor protein
- The adaptor protein binds the cargo
- Clatherin binds to the adaptor protein
What mediates interaction between transport vesicles and target membranes?
Tethering factors
Rab proteins (small-GTP binding porteins)
What three things drive membrane fusion?
vSNARES
tSNARES
Dynamin
How do vesicles dock?
Active Rab proteins bind membrane tethering factors
Tethering factors bind coat proteins and the coat is removed.
How do vesicles fuse?
The membranes are pulled together and fused via vSNARES and tSNARES interacting
What is the mechanism of vSNARE and tSNARE interaction?
SNARE proteins have a central coiled-coil domain
Responsible for zipping the two SNARES together
What are lysosomes?
membrane-enclosed organelles containing enzymes to break down all types of biological polymers
What are lysosomal storage diseases?
Diseases that result from mutations in lysosomal enzymes
undegraded material accumulates in the lysosomes
Most lysosomal enzymes are…?
Acid Hydrolases active at pH 5
What is the significance of lysosomal enzymes only being active at pH 5?
Prevents cell contents digestion if the lysosome membrane breaks down
How does material for digestion get into the cell?
Endocytosis
How are lysosomes formed?
When transport vesicles fuse with a late endosome
What two pathways intersect at endosomes?
Secretory and endocytic pathways
What is the function of early endosomes?
Fuse with endocytic vesicles from PM
Separate molecules for recycling from molecules destined for degradation in lysosomes
What is the function of recycling endosomes?
Serve as a site for molecules that are to be transported back to the plasma membrane
What is the function of late endosomes?
Carry molecules to be degraded by lysosomes
What happens during the maturation of late endosomes?
Transport vesicles carrying acid hydrolases fuse with late endosomes, forming lysosomes
What are phagolysosomes?
Specialized lysosomes in phagocytic cells
What is autophagy?
Digestion of the cell’s own components
What normal roles does autophagy play?
Nutrient starvation - reutilized nonessential cellular components
Apoptosis
