Vesicles and secretion 2 Flashcards
(41 cards)
What is the most common vesicle type from the trans-Golgi?
Clathrin-coated vesicles.
What is the structure of clathrin-coated vesicles?
Clathrin triskelions on the outside, adapter protein (AP) complexes inside.
Which small GTPase is required for clathrin/AP coat assembly?
ARF.
What does Dynamin do during vesicle formation?
Forms a ring around the neck and pinches off the vesicle via GTP hydrolysis.
What is needed for clathrin uncoating?
Auxillin and ATP hydrolysis by Hsp70 (Hsc70).
Why is uncoating of clathrin necessary?
To expose v-SNAREs for membrane fusion.
What are the two pathways for targeting proteins to lysosomes?
Directly via AP3 or via late endosomes with clathrin/AP complexes.
What modification is key for lysosomal targeting?
Phosphorylation of mannose-6 in the cis-Golgi.
What enzyme adds P-GlcNAc to lysosomal proteins?
GlcNAc phosphotransferase.
What receptor recognizes M6P-modified proteins?
Mannose-6-phosphate receptor (M6PR).
How are proproteins activated?
By proteolytic cleavage, often after the Golgi.
What are common cleavage sites in proproteins?
Dibasic residues like arginine (R) or lysine (K).
What is the function of furin?
An endoprotease that activates proproteins.
Where does furin cleave the SARS-CoV-2 spike protein?
At a dibasic cleavage site.
How are proteins sorted to apical vs basolateral membranes?
Via Rab/v-SNARE differences or transcytosis.
What is transcytosis?
Endocytosis followed by delivery to another membrane region.
What is receptor-mediated endocytosis?
Uptake of molecules bound to cell-surface receptors.
What coat is used in receptor-mediated endocytosis?
Clathrin with AP2.
What particles are taken up via LDL receptor?
Lipoprotein particles.
What does the LDL receptor bind?
Lipoproteins and AP2 via a cytoplasmic sorting signal.
What causes release of LDL in late endosomes?
Low pH protonates histidines in the receptor.
What enzyme acidifies endosomes and lysosomes?
V-class H+ ATPase.
Why is chloride entry needed during acidification?
To prevent buildup of electric potential.
What triggers release of LDL from its receptor?
Histidine protonation at low pH.
