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17 Cards in this Set

  • Front
  • Back
ER-Golgi Transport
COPII anterograde vesicles form around vesicles (the cargo receptors are embedded in these proteins. Decoating exposes vSNARE and tSNARE interaction and vesicular fusion. COPI use identical process except going backwards
KDEL Signal and Golgi-ER Transport
KDEL signal is a mechanism for getting ER proteins back to the ER after they have been carried in a vesicle to the Golgi. Missorted ER resident proteins have a KDEL binding sequence that will bind the KDEL protein (in the vesicle membrane) only at lower pH's like those in the Golgi compared to the ER. They go back via COPI coated vesicles and the interaction ceases at the more neutral pH of the ER
GTPase Function in vesicle coating and decoating. Sar1 and ARF.
GTP-bound form of GTPase
(Sar1 or ARF) inserts into donor
vesicle membrane thru its
hydrophobic N-terminal domain. These serve a few functions: binding for coat assembly, curvature of vesicles, some recruitment of cargo. The hydrolysis of the bound GTP promotes coat disassembly and exposing of SNARE proteins
Golgi Processing: High Mannose vs. Complex Glycosylation
Glycoproteins transported from ER to cis-Golgi as (Man)8(GluNAc)2
High Mannose Glycosylation. This is further processed in the Golgi to become complex glycosylation
Vesicle Transport from Trans-Golgi Network; different coats for different destinations (IMPORTANT: M-6-P)
1. Retrograde transport: COPI, ARF (GTPase), no clathrin
2. Lysosome: Clathrin?, ARF/AP3, IMPORTANT: M-6-P signal, if it is not created properly, problems with transport to the lysosome
3. Endosome: Clathrin/AP-1/ARF
4. Constitutive secretion: Unknown
5. Regulated secretion: Unknown, aggregation mechanism
Clathrin Coat
3 Heavy chains, 3 Light chains, interwoven to form triskelion structure (looks like soccer ball)
A patient presents with features similar to Downs syndrome, presence of dense inclusion bodies in skin cells. Lysosomal Trageting – Final Result (Clinical Case)
Phosphate group on mannose, binds a receptor that interacts with AP, then clathrin coats it. Low pH causes the protein to dissociate, the receptor may go back.
 It may also go to plasma membrane to get mannose-6-phosphate proteins that may have gotten out. 
If protein doesn't have M-6-P, it will constantly get secreted. This is the clinical issue with the patient.
Mucolipidosis II (I-Cell Disease) and the M-6-P signal
In the disease, the enzyme GlcNAc phosphotransferase is blocked. Therefore in I-cell disease, the phosphate group can't be added to the Mannose, essentially. Not sure exactly why the enzyme doesn't work as it should, but it doesn't. A large group of lysosomal enzymes do not get targeted to lysosome as they should.
Mucolipidosis in general
Many have problems with one enzyme involved in the lysosome, so only one thing inparticular is not broken down inside the lysosome, whereas I-cell and pseudo-Hurler's have lysosomal targeting problems, so lots of stuff is screwed up.
The key to MLII (I-cell disease) and MLIII (pseudo-Hurler polydystrophy)
Deficiency in GluNAc-1-phosphotransferase → no M-6-P modification →
multiple lysosomal enzymes mistargeted and secreted → multiple type
inclusions in lysosome (primarily carbohydrates and lipids).
Mucolipidosis types II and III
I-cell disease
Pseudo-Hurler Polydystrophy

Mucopolysaccharidosis type I

Mucopolysaccharidosis type II

Mucopolysaccharidosis type III = Sanfilli!!!

Heparan-N-sulphatase (A)
α-N-Acetylglucosaminidase (B)
AcetylCoA:N-acetyltransferase (C)
N-Acetylglucosamine 6-sulphatase (D)
Lipid Storage Disorders
Gaucher (El Gaucho is a fatso = lipid storage)

Glucocerebrosidase (β-glucosidase)
GM2 - Gangliosidosis type I

β-Hexosaminidase A
GM2 - Gangliosidosis type II
Sandhoff disease

β-Hexosaminidase A & B