Block2 2.er-Golgi Ii – Secretory Pathway

Front 1

ER-Golgi Transport

Back 1

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

Front 2

KDEL Signal and Golgi-ER Transport

Back 2

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

Front 3

GTPase Function in vesicle coating and decoating. Sar1 and ARF.

Back 3

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

Front 4

Golgi Processing: High Mannose vs. Complex Glycosylation

Back 4

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

Front 5

Vesicle Transport from Trans-Golgi Network; different coats for different destinations (IMPORTANT: M-6-P)

Back 5

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

Front 6

Clathrin Coat

Back 6

3 Heavy chains, 3 Light chains, interwoven to form triskelion structure (looks like soccer ball)

Front 7

A patient presents with features similar to Downs syndrome, presence of dense inclusion bodies in skin cells. Lysosomal Trageting – Final Result (Clinical Case)

Back 7

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.

Front 8

Mucolipidosis II (I-Cell Disease) and the M-6-P signal

Back 8

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.

Front 9

Mucolipidosis in general

Back 9

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.

Front 10

The key to MLII (I-cell disease) and MLIII (pseudo-Hurler polydystrophy)

Back 10

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).

Front 11

Mucolipidosis types II and III

Back 11

I-cell disease
Pseudo-Hurler Polydystrophy

N-acetylglucosamine-1-
Phosphotransferase

Front 12

Mucopolysaccharidosis type I

Back 12

Hurler-Scheie

α-L-Iduronidase

Front 13

Mucopolysaccharidosis type II

Back 13

Hunter

Iduronate-2-sulphatase

Front 14

Mucopolysaccharidosis type III = Sanfilli!!!

Back 14

Sanfillipo

Heparan-N-sulphatase (A)
α-N-Acetylglucosaminidase (B)
AcetylCoA:N-acetyltransferase (C)
N-Acetylglucosamine 6-sulphatase (D)

Front 15

Lipid Storage Disorders

Back 15

Gaucher (El Gaucho is a fatso = lipid storage)

Glucocerebrosidase (β-glucosidase)

Front 16

GM2 - Gangliosidosis type I

Back 16

Tay-Sachs

β-Hexosaminidase A

Front 17

GM2 - Gangliosidosis type II

Back 17

Sandhoff disease

β-Hexosaminidase A & B