Protein targeting and protein degradation Flashcards
1
Q
preprotein (proteolytic processing)
A
- protein precursor that contains a signal pepetide sequence that is cleaved
- longer ones are more commonly removed because they can affect folding
- occurs in ER
2
Q
signal anchor sequences
A
- signal sequences that are rich in hydrophobic amino acid residues to help anchor transmembrane proteins
3
Q
Nuclear Localization sequences
A
- short sequences in proteins destined for the nucleus
- do not get cleaved
4
Q
proprotein
A
- proteins initially synthesized as large precursor proteins and need to be proteolytically trimmed to become active
5
Q
what is the difference between a preprotein and a proprotein
A
- preproteins have a signal sequence that needs to be cleaved
- proproteins are inactive until modification (usually cleavage) activates them
- cleavage occurs in the ER
6
Q
What types of proteins are targeted to the ER?
A
- membrane proteins
- secreted proteins
- lysosomal proteins
- proteins that need posttranslational modification
- removal of signal sequences, glycosylation (mostly N-linked)
- nuclear, mitochondrial, and chloroplast proteins do not go through the ER
7
Q
Explain how ER targeting works
A
- a signal recognition particle (SRP) binds the emergent signal sequence and the ribosome
- SRP binds GTP which pauses elongation
- ribosome/SRP complex binds to receptors on the face of the ER
SRP hydrolyzes and GTP dissociate - translation resumes
- signal sequence is cleaved and full protein is translocated into the ER
8
Q
how does glycosylation affect a protein?
A
- can change polarity and solubility (carbohydrates are polar)
- serve as marker protein
- structural complextiy
- facilitate cell-cell interactions
9
Q
location of N-linked vs O-linked glycosylation
A
- N-linked occurs in the ER
- O-linked occurs in the golgi
10
Q
how does N-linked glycoslyation work?
A
- it is done by transferase only found in the lumen of the ER
- oligosaccharide core transferred to the protein
- core can be modified in different ways for different proteins
11
Q
How does golgi sorting work
A
12
Q
After proteins leave the ER, do they go directly to their final destination? If not, where do they go and what happens to proteins there?
A
- no, they go to the golgi to get sorted
- golgi sends them to their final destination
13
Q
what do rab proteins do?
A
- they are recruited to the vesicle and interact specifically with particular acceptor compartment membranes
- rab proteins on the vesicle are recognized by specific tethering proteins on the acceptor
14
Q
what do SNARE proteins do?
A
- v-SNARE on vesicle and t-SNARE on acceptor recognize each other
- triggers membrane fusion
15
Q
4 steps of protein transport
A
- budding
- transport
- docking
- fusion
19
Q
what does the proteasome do
A
- degrades proteins with K48 ubiquidation
20
Q
two subcomplexes of the proteasome
A
- core particle
- protease activity - regulatory particles
- recognition of ubiquitin chain
- has ATPases that likely function in protein unfolding and translocation into the core
- de-ubiquitination
