Lecture 12 Flashcards
SLIDE 3
SLIDE 4
in COPII-coated
vesicles, where do cargos bud from
what are the exit signals for cargos?
Cargo packaged in COPII-coated vesicles
➢vesicles bud from ER exit sites
Cargo often has exit signals:
➢soluble proteins are bound by cargo receptors
➢transmembrane proteins are bound by the COPII coat
Other cargo has no exit signal, but are packaged because of high concentration in the ER
how does the Cargo go from the ER to the cis Golgi Network
- COPII-coated vesicles bud from the ER exit site, and then shed their COPII coat
- Fuse with each other to form vesicular tubular clusters
- Vesicular tubular clusters move to the Golgi apparatus via motor proteins
how does retrieval (retrograde) transport work:
- what vesicles are used for this transport
- Retrieval transport occurs using COPI-coated vesicles
- Vesicles from vesicular tubular clusters and the Golgi go to the ER
Vesicles contain:
* escaped ER resident proteins
* proteins involved in vesicle budding from ER
how does retrieval (retrograde) transport work:
- pathway with ER resident proteins
- protein that is supposed to be in the ER but are mistakenly in the vesicle can be retrieved
- Many ER resident proteins have ER retrieval signals
- Soluble ER proteins have a retrieval signal (KDEL), and are bound by the KDEL receptor
➢Packaged into COPI-coated transport vesicles - ER membrane proteins have a retrieval signal
- E.g., of signal = KKXX at C-terminus
➢Signal is bound by COPI coats
➢Packaged into vesicles
how does pH play a role in retrieval of ER resident proteins from golgi
KDEL receptor cycles between ER and Golgi
* at vesicular tubular clusters, Golgi = high affinity for KDEL
* at ER = low affinity for KDEL
This is due to regulation by pH (V-type ATPase H+ pump)
* Binds KDEL with KDEL receptor very tightly in acidic pH in golgi.vesicular tubular clusters; releases in neutral pH when transported back into ER
what are other methods of retrieval mechanisms if there is no retrieval signal on ER and golgi resident proteins
- Not all ER and Golgi resident proteins have retrieval signals, but the proteins end up in the right compartment
- Other Possible mechanisms for retrieval:
1. Different transport rates
➢E.g., some Golgi enzymes cycle between the ER and Golgi, but
transport to the ER at a slower rate
2. Proteins retained in resident compartment
➢proteins that function in the same compartment form large complexes,
which prevents packaging into transport vesicles
complete
- Transport through Golgi cisternae to trans Golgi network (TGN)
- Transport vesicles are kept close to Golgi cisternae by tethering proteins
- Processing of N-linked oligosaccharides occurs in the Golgi
slide 12 model 1
slide 13 model 2
can both models for Transport of Proteins through the Golgi Cisternae occur?
Both models may occur:
* Some cargo move rapidly by transport vesicles
* Other cargo move more slowly through cisternal maturation
what is the TGN
vesicle is trafficked from TGN
- TGN: complex network of membranes & vesicles
- Major branch point
- Proteins sorted into different vesicles
how is Vesicular Transport from TGN to the Lysosome
slide 17 REVIEW
- Vesicles from TGN transported to late endosome
- late endosomes gradually mature into lysosomes, which break down and can be resued?
- Cargo = lysosomal hydrolases
- Needed for lysosome function and degradation of macromolecules
REVIEW
what is the lysosome and what does have? REVIEW
- the lysosome is the site of intracellular digestion
Acid hydrolases:
* synthesized in the ER and
processed in the Golgi
* degrade macromolecules (ex. nucleases, proteases, lipases etc)
* active at acidic pH
