Lecture 13 Flashcards
What are the basic features of vesicular transport?
Directional transport via vesicles carrying cargo by budding and fusion
Biosynthetic-secretory pathway
Vesicles synthesized and transported within the cell
Endocytic pathway
Vesicles are endocytosed from outside the cell and are coming into the cell
Retrieval pathway
Vesicles are returning particles to their original compartment
What are the 2 major functions of coating for vesicles?
- Concentrates select proteins for transport
2. Molds vesicle to form to specific shape
Where do COPI and COPII mediate transport?
From ER and Golgi cisternae
Where do Clathrin-coated vesicles mediate transport?
From Golgi apparatus and plasma membrane
Clathrin
Basket-like structure of triskelions that form coated pits on cytosolic side of the membrane
Adaptor proteins
Bind clathrin and membrane-bound cargo receptors
When is clathrin coat lost?
After vesicle formation is complete
Phosphoinositides (PIs)
Control recruitment and binding of proteins to specific organelles/domains; regulate vesicular trafficking
BAR domains
Responsible for membrane bending as vesicle is forming
Dynamin
Protein that assembles a ring around clathrin bud which tethers (PIP2) and pinches off (GTPase) vesicle
What is the role of Hsp70 in the removal of the clathrin coat?
Peels off coat using ATP
Rab proteins
Direct vesicle to specific spots on target membrane
SNARE proteins
mediate fusion of vesicle with membrane
Rab-GDP dissociation inhibitor (GDI)
Keeps Rab in GDP-bound, inactive, soluble form
Rab-GEFs
Keep Rab in GTP-bound, active form that is tightly bound to membrane
Rab Effectors
Bind active Rab proteins present on target membrane to facilitate tethering and fusion
Rab1
Located in ER and Golgi complex
Rab2
Located in cis-Golgi network
Rab3A
Located in synaptic vesicles, secretory vesicles
v-SNAREs
Single polypeptide found on vesicle membrane
t-SNAREs
2-3 proteins found on target membranes
COPII coated vesicles
Bud off from ER exit sites; proteins display exit signals and recognized by receptors on COPII coat
What occurs after vesicles bud from ER exit sites?
Shedding of the coat, fusion of the naked vesicles via SNARE proteins; become vesicular tubular structures
What coat is used for vesicles in the retrieval pathway?
COPI
KKXX sequence
ER retrieval signal present in ER membrane proteins; interacts with COPI and is packaged into COPI coated vesicles
KDEL sequence
ER retrieval signal present in soluble proteins; packages them into COPI coated vesicles
Cis-Golgi Network
Fused vesicular tubular clusters arriving from ER (proteins and lipids enter here)
Trans-Golgi Network
Region that allows exit of proteins and lipids to next step of secretory pathway
Cisternal Maturation Model vs. Vesicle Transport Model
Maturation of Golgi constantly occurring as vesicles are transported vs. Golgi is established structure that vesicles are just moving through; reality: Both
