Lecture 10 and 11 Flashcards
What does vesicle trafficking mediate?
Constant flow of proteins throughout the cell
What goes through the retrieval pathway?
Retrograde trafficking
- Golgi –> ER
- Late endosome –> Golgi
- Early endosome –> Golgi
- Secretory vesicles –> Golgi
- Early endosome –> Cell exterior
What goes through the endocytic pathway?
- Cell Exterior –> Early Endosome
- Early Endosome –> Late Endosome
- Late Endosome –> Lysosome
What goes through the biosynthetic/secretory pathway?
- ER –> Golgi
- Golgi –> Late Endosome
- Golgi –> Early Endosome
- Golgi –> Cell Exterior
- Golgi –> Secretory Vesicles
- Late Endosome –> Lysosome
- Secretory Vesicles –> Cell Exterior
What does the golgi apparatus/complex consist of?
Specific orientation of flattened stacked membrane compartments (cisternae; 4 to 6 cisternae per stack) that “mature” over time
What is the golgi apparatus/complex divided into?
- Cis-face: Entry face at beginning of golgi (near ER)
- Medial: Sandwiched by cis and trans cisternae
- Trans-face: Exit face just prior to leaving golgi
How do proteins enter the golgi apparatus/complex?
Through the cis golgi network (CGN)
How do proteins exit the golgi apparatus/complex?
Through the trans golgi network (TGN)
Where are proteins post-translationally modified in the golgi?
In various sub-compartments
What are the two models for golgi maturation?
Vesicle transport and cisternal maturation
What is involved in the vesicle transport model?
- Golgi is static and enzymes remain in each location
- Vesicles fuse and leave the structures in sequence
What is involved in the cisternal maturation model?
- Golgi structure is dynamic and entire cisternae move
- Cis-cisternae eventually become mid-cisternae and then trans-cisternae
Why do we need retrograde flow back into cis-cisternae?
Because processing enzymes have to make their way back to where they started
What are coat proteins?
Proteins which “coat” or cover the vesicle
What types of coat proteins are there?
- Clathrin
- Coat protein I (COPI)
- Coat protein II (COPII)
What does the presence of a particular coat protein depend on?
Where the vesicles originate from
Where does clathrin originate from?
Transport vesicles from plasma membrane and between endosomal and golgi compartments
Where does COP I originate from?
Bud off from Golgi
Where does COP II originate from?
Early transport vesicles from ER
What is each clathrin subunit composed of?
Three large (heavy) chains and three small (light) chains that form triskelion
What do triskelions form?
Combinations of hexagons and pentagons (polyhedral cages)
What is clathrin attached to?
Adaptor molecules in the cell membrane
When does the clathrin coat form from the triskelion structure?
Upon endocytosis
When is the clathrin coat shed?
Prior to vesicle fusion and transport
What do adaptor proteins form?
A second coat around vesicles
What does the adaptor protein coat do?
Serves to anchor cargo receptors into the vesicle
What does each type of adaptor recognize?
Different receptors
What are the key regulatory molecules of vesicle trafficking?
Phosphatidyl inositol phosphatases (PIPs)
What do different PIs bind?
Different proteins
Where do distinct sets of phosphatases and kinases reside in?
Different vesicle populations
Why do distinct sets of phosphatases and kinases reside in different vesicle populations?
To alter PI molecules
What does the presence of different phosphoinositide molecules at certain membrane regions do?
Regulate protein binding in those regions
What is required for vesicle fusion?
Energy
What is required to assist in membrane fusion?
Dynamin
What domains does dynamin have?
PIP2 binding domain and GTPase domain
What diseases are caused by dynamin mutations?
- Charcot Marie Tooth (CMT) disease
- Centronuclear myopathy (CNM) disease
- Some forms of epilepsy
What is Charcot Marie Tooth (CMT) disease?
A progressive nerve disease
- Named after the 3 doctors who discovered it in 1886
- 1 in 2,500 births
- Leads to loss of myelin sheath and peripheral nerve damage
What does centronuclear myopathy (CNM) disease cause?
Muscle weakness that can range from mild to severe (dynamin 2 gene)
What are COPI and COPII vesicles?
Other regulatory molecules that control vesicle formation and recruit coat proteins to specific membrane regions
What do coat recruitment GTPases do?
Control when and where clathrin and COP coated vesicles are formed
What are Arfs?
ADP ribosylation factors
- GTPase which is myristoylated at the N-terminus (anchors to membrane)
- Responsible for clathrin and COPI vesicle formation
What is Sar1?
Secretion-associated and Ras-related
- When bound to GTP, Sar1 can bind to cytoplasmic face of membrane
- When in membrane, it recruits COPII coat proteins (Secs)
What forms the inner COPII coat?
Sec23/24
What forms the outer COPII coat?
Sec 13/31
What do mature COPII vesicles contain?
Sar1, Sec 23/24, and Sec 13/31
- Dynamin does not appear to be required for scission of the vesicle for COP coated vesicles
When do COPII proteins dissociate?
Upon release of the vesicle
