Lectures 13&14 - Protein Trafficking Flashcards
What is the anterograde pathway
Forward - ER to Golgi, Golgi to plasma membrane
What is the retrograde pathway
Retrieval - Golgi to ER eg.
How do molecules move from one organelle to the next
1) Vesicle buds from donor compartment
2) Vesicle pinches off and translocates
from donor to acceptor compartment
3) Vesicle docks with acceptor compartment
4) Vesicle fuses with acceptor compartment releasing contents into lumen
How do buds form
Driven by the assembly of protein coats onto membrane
What is a Cathrin Coat
a protein that coats vesicles - made of Cathrin proteins and ‘adaptor’ proteins)
What is the triskelion structure
Three clathrin molecules join at a common hub to form a three-legged “triskelion”, which is the basic building block of the coats.
Animation 15.5 on Cathrin coat formation - can form cages
What are the processes in pinching off
Fission and scission
Scission event is carried out by a protein called dynamic that separates the membrane associated with the vesicle and the rest of the membrane
What pathways are associated with clathrin coats
Budding from the Golgi and from pasta membrane are associated with clathrin coated vesicles
What other types of coat are there
COPI and COPII coats (involved in retrograde trafficking and ER respectively)
What is clathrin coats used for
budding from the plasma membrane (endocytosis) and from the Golgi netowrk
What are COPII coats involved in
Anterograde transport from the ER.
What are COPI coats involved in
Retrograde transport from gold apparatus
In a clathrin-coated vesicle with coat proteins clathrin and adaptin 1 - where is the origin and the destination
O - Golgi apparatus
D - Lysosome (via endosomes)
In clathrin coated vesicles with clathrin and adaptin 2 - where is the origin and where is the destination
O - Plasma Membrane
D - Endosomes
In COP-coated proteins, made from COP proteins - what is the origin(s) and the destination
O1 - ER D1 - Golgi apparatus
O2 - Golgi cisterna D2- Golgi cisterna
O3 - Golgi apparatus D3 - ER
What controls coat formation
Coat recruitment GTPases
How is cargo selected
Active recruitment
Selective exclusion
Passive inclusion
What is bulk sorting
Molecules are passively included in vesicles (bulk sorting)
How does budding from the ER occur
Some proteins are selectively recruited into buds. For example some integral membrane proteins have cytoplasmic domains that will interact with coat proteins. This will concentrate them into buds. Lumenal cargo proteins can also be selectively recruited into buds bey interacting with cargo receptors –that span the ER membrane and interact with coat proteins. The cargo and coat are indirectly linked via protein-protein interactions.
Some proteins are excluded from entering budding vesicles-for example proteins that mis-fold in the ER.
Some proteins are passively included in the budding vesicle. Some of these proteins may need to be returned to the ER.
What is a DXE motif
Diacidic motifs consist of two acidic amino acid residues, separated by any other amino acid
How are vesicles uncoated
Vesicle uncoating is mediated by phosphorylation of adaptor subunits. The phosphatases involved are recruited to the vesicle by chaperone proteins such as Hsc70 and auxilin.
slide 19
Why many some proteins be excluded from budding vesicles
Antibodies do not get packaged into ER transport vesicles until they are correctly assembled. The ER can be considered as a ‘quality control’ station in the secretory pathway.
