Where do transmembrane proteins in the ER face?
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The outside of the cell.
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Where do transmembrane proteins in the ER face?
The outside of the cell.
What is the role of GTPases?
They function in vesicle formation.
What is the role of clathrin in cellular processes?
It is required for receptor-mediated endocytosis.
What are the main outcomes of the Unfolded Protein Response?
Restoration of normal ER function, degradation of misfolded proteins, and, if stress persists, apoptosis.
What triggers Ire1p oligomerization?
Accumulation of unfolded proteins in the ER.
What does COPII transport?
From the ER to the Golgi.
At which membranes do COPI and COPII function instead of clathrin?
Golgi and plasma membrane (PM).
What variation exists in Rab GTPases?
Variation in Rab C-terminal tails.
What happens when GTPase is activated?
Hydrophobic tail exposure occurs.
What happens to HAC1 u mRNA when Ire1p is activated?
It is spliced to form HAC1 i mRNA, which is then translated into Hac1p i.
What type of protein is Dynamin?
A GTPase.
What is the role of SNARE proteins in vesicular transport?
They guide vesicular transport by directing vesicles to the correct place.
What is a characteristic of at least one t-snare?
It is an integral-membrane protein.
Which complex is involved in the extraction of ubiquitylated misfolded proteins from the ER?
The Cdc48 Ufd1 Npl4 complex.
How does IRE1 contribute to the UPR?
It senses unfolded proteins and activates splicing of XBP1 mRNA, leading to the production of a transcription factor that enhances the expression of chaperones.
What does GAP stand for?
GTPase Activating Protein.
What role does adaptin play in vesicle formation?
Adaptin binds clathrin and receptors, acting as a bridge.
Can vesicles be tubular?
Yes, vesicles can be tubular.
What does ubiquitylation trigger in the context of misfolded proteins?
It triggers their retro translocation to the cytosol.
What role does PERK play in the UPR?
It phosphorylates eIF2α, reducing general protein synthesis and allowing selective translation of stress response proteins.
What is the difference between SMAP1 and SMAP2 regarding their regulation?
SMAP2 appears to be a regulator of Arf1 in vivo, unlike SMAP1.
What do the letters 'V' and 't' represent in the context of SNAREs?
'V' stands for vesicle and 't' stands for target SNAREs.
How many polypeptides make up one clathrin?
6 polypeptides (3 large and 3 small).
How many members are involved in binding particular vesicles?
30 members.
What is another variation found in Rabs?
Variation in effectors.
What is Ire1p?
A transmembrane serine-threonine kinase in the ER.
With which protein does SMAP2 interact?
Clathrin heavy chain (CHC) and clathrin assembly protein CALM.
What is the primary function of vesicular trafficking?
To allow proteins and vesicles to reach their destinations.
What is a consequence of protein misfolding?
Aggregation.
What is the effect of neural toxin proteases on neuronal snares?
They target and affect neuronal snares, as seen in botulism.
Which GTPase is associated with COPI?
ARF.
What is the newly identified homologue of SMAP1?
SMAP2.
How does protein misfolding relate to Alzheimer's disease?
It leads to the formation of amyloid plaques and neurodegeneration.
What is the role of ubiquitylation in the ER-associated degradation (ERAD) process?
It is required for different steps of the ERAD process, facilitating the extraction of misfolded proteins from the ER membrane.
What do GEFs determine in the vesicle budding process?
When the vesicle is ready to bud.
What do GAPs trigger in GTPases?
GTPase inactivation.
What is the role of Dynamin in vesicle formation?
Dynamin forms a ring around the bud.
What role do prions play in disease?
They cause neurodegenerative diseases through misfolded proteins.
What is a coiled-coil structure in snares?
A tightly intertwined set of 4 α-helix domains.
What role do Rab GTPases play in vesicular trafficking?
They ensure the specificity of vesicular docking.
What is the role of Hac1p i?
It is a transcriptional activator that upregulates UPR target genes.
How do calnexin and calreticulin interact with glycoproteins?
They bind to the monoglucosylated oligosaccharide and hydrophobic segments of the unfolded glycoprotein in their ATP-bound state.
What structure do vesicles use for transport during exocytosis?
The Actin Cytoskeleton.
What are snares?
Integral-membrane proteins that pull membranes together.
What prevents uncoating at membranes?
Specific mechanisms at the membranes prevent uncoating.
What role do GTPases play in vesicle trafficking?
They are required for vesicle formation and fusion.
What is the consequence of GTPase inactivation?
It falls off the membrane and triggers coat disassembly.
What activity does SMAP2 exhibit?
GAP activity, similar to SMAP1.
What role do SNARE proteins play in cellular processes?
They promote membrane fusion.
What are the two different processes involved in vesicle transport?
Vesicle budding and vesicle fusion.
How many α-helix domains are contributed by t-snares and v-snares?
Three by t-snares and one by v-snare.
Which GTPase is associated with COPII?
Sar.
How do Rabs differ from coat assembly GTPases?
Rabs are different from coat assembly GTPases (ARFs).
What enzyme rejoins the exons of HAC1 mRNA?
Rlg1p (tRNA ligase).
What does the SMAP gene family represent?
An important ArfGAP subfamily with common and distinct functions in vesicle trafficking.
What is the primary function of vesicular trafficking?
To allow proteins and vesicles to reach their destinations.
Where do transmembrane proteins in the ER face?
The outside of the cell.
What is exocytosis?
The process by which vesicles transport substances out of a cell.
What does GEF stand for?
Guanine Nucleotide Exchange Factor.
Which diseases are associated with protein misfolding?
Prion diseases and Alzheimer's disease.
What does COPI transport?
From Golgi to Golgi.
How do vesicle-surface markers function in vesicular transport?
They direct vesicles to the correct location.
Which proteins are involved in uncoating the vesicle?
Hsp70 chaperone and auxillin.
What is a Triskeleion composed of?
3 large and 3 small polypeptides.
Where do Rabs interact with SNAREs?
On the cytoplasmic face.
How does modification with ubiquitin chains assist misfolded proteins?
It guarantees guidance, recognition, and binding to the proteasome for efficient degradation.
What is the Unfolded Protein Response (UPR)?
A cellular stress response related to the endoplasmic reticulum (ER) that aims to restore normal function by halting protein translation and activating the signaling pathways that lead to increased production of molecular chaperones.
What triggers GTPase activation?
GEF activation.
Which proteins are primarily involved in the UPR?
IRE1, PERK, and ATF6.
What happens if the UPR fails to resolve the stress?
It can lead to cell death through apoptosis.
What does Ire1p do to HAC1 mRNA?
Cuts it at two sites, removing a nonclassical intron.
What is the role of SMAP1?
It is a GTPase-activating protein (GAP) for Arf6 that regulates clathrin-dependent endocytosis of transferrin receptors.
What effect does overexpression of SMAP2 have?
It delays the accumulation of TGN38/46 molecule on the TGN.
What pathway does SMAP2 function in?
The retrograde, early endosome-to-TGN pathway in a clathrin- and AP-1–dependent manner.
What triggers the dissociation of glycoproteins from calnexin/calreticulin?
The action of glucosidase II removing the terminal glucose and a change in affinity of the polypeptide binding site.
What triggers the Unfolded Protein Response?
The accumulation of misfolded or unfolded proteins in the endoplasmic reticulum.
Where is the amino terminus of Ire1p located?
In the ER lumen.
Where does SMAP2 colocalize?
With adaptor proteins for clathrin AP-1 and EpsinR on early endosomes/trans-Golgi network (TGN).
What does Hac1p i bind to in order to activate gene expression?
The unfolded protein response element (UPRE) in gene promoters.
What happens if folding does not occur rapidly after glycoprotein dissociation?
The glycoprotein is reglucosylated by UDP-glucose:glycoprotein glucosyltransferase.
What happens to Asn residues in nascent polypeptide chains as they enter the ER?
They are glycosylated with an oligosaccharide of composition Glc3Man9GlcNAc2.
What is the role of glucosidases I and II in the glycosylation process?
They rapidly remove the outermost two glucoses to reveal the monoglucosylated species.
What is the function of the binding and release cycle of calnexin/calreticulin?
What role does ERp57 play in the protein folding process?
It catalyzes disulfide bond formation and isomerization within the glycoprotein.
