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ER Lumen modifications
- a) Removal of signal sequence
- b) Oxidation of sulfhydryl groups
- c) N-Glycosylation
- d) Attachment of GlycosylPhosphatidyl-Inositol (GPI) anchor (some proteins)
- e) Protein folding by chaperones
- Squares = N-acetylglucosamine (G IN Ac)
- Green Circles = Mannose
- Blue Circles = Glucose
Aspargine - Any - Serine or Threonine
BiP - Binding Immunoglobulin Protein Role
Recognizes incorrectly folded protein by binding to exposed AA that would normally be buried in the interior of correct polypeptide or polypeptide that have not yet been assembled into their correct oligomeric structure.
Class - Lectins: Bind specifically to particular carbohydrate residues
Binds to oligosaccharides on proteins that have not yet folded completely and keeps them in the ER until correct folding or sends them to the cytosol for degradation.
Example folding procedure involving calnexin
- 1) Unfolded protein w/ 3 glucose that undergoes glucose trimming leaving 1 glucose.
- 2) Protein binds to Calnexin and glucosidase removes protein from Calnexin and removes glucose.
- 3) If folded correctly, protein exits ER. If not, it binds to glucosyl transferase and gets one glucose attached to redo the cycle.
Secretory System Pathway
Because proteins utilizing secretory pathway pass ER, signals are required.
Experiment that determined secretory system is Pulse/chase experiment by Palade.
1. Pulse a dye or signal in a pathway for a short time.
2. View movement of signal/dye (chase).
Green fluorescent protein (GFP) fusion protein
A method to study transit of protein through cell.
- 1. Use genetic engineering to fuse cDNA encoding GFP to cDNA encoding protein.
- 2. Fluorescent marker now exist on protein.
Vesicular Stomatitis Virus
- 1. Virus starts at ER
- 2. Exits ER
- 3. Goes through Golgi
- 4. Moves through plasma membrane
Ordered series of compartments called cisternae.
Transit through the secretory system is ________
Vesicular (i.e. leaves donor compartment as budding and enters target compartment as fusion)
High mannose (mannose tail 1-2-2-1)
Complex: has row of GINAc, galactose, NANA
Carbohydrate units _______ from the _________ and __________ from __________
Protrude, glycoprotein, protect, degradation
Golgi apparatus layers
- 1. Cis Golgi Network
- 2. Cis Cisterna
- 3. Medial Cisterna
- 4. Trans Cisterna
- 5. Trans Golgi Network
Cis Golgi Network Role
Sorting: Phosphorylation of oligosaccharides on lysosomal proteins.
Golgi Stack Role
Cis: Removal of MAn
Medial: Removal of Man and addition of GlcNac
Trans: Addition of Gal and NANA
Trans Golgi Network Role
Sorting: Sulfation of tyrosines and carbohydrates.
Protein goes to lysosome, plasma membrane, or secretory vesicle.
Vesicular tubular cluster
Acts as cargo mover and intermediate between ER and cis Golgi network.
COPII coated vesicle of proteins find their way to VTC.
COPI coated vescile of proteins find their way back to ER for Golgi network
Retention of resident proteins of compartments
Soluble ER protein binds to KDEL where membrane KDEL receptors bind and keep ER proteins contained.
Main site of digestion of intracellular and extracellular debris including macromolecules and obsolete parts of the cell.
Enzyme class and examples?
Evolution from ______?
- Acid Hydrolase
- - Nucleases, proteases, lipases, glycosidase, phosphatases, sulfatases, phospholipases.
ATP dependant hydrogen pump
Plant lysosome are called _______
Lysosomes morphology are _________
Regions of protein sequence that, when the protein is folded, signals the protein to be binded by a receptor protein in the cis-Golgi to undergo processing.
Receptor is called GlcNAc phosphotransferase
GlcNAc phosphotransferase and pathway of substrate
Binds UDP-GlcNAc to proteins destined for lysosome and is the complex is bridged by a phophate group.
Goes through medial and trans-Golgi where GlcNac will be removed and expose phosphorylated mannose.
Golgi to Lysosome pathway
Inclusion Cell Disease
Single gene defect and recessive.
Hydrolytic enzymes of lysosomes in fibroblast missing. Patients exhibit lots of inclusion bodies (garbage in cells).
Elizabeth Neufeld found out that if you put defective fibroblast with regular fibroblast, defective fibroblast recovered.
They lacked functional GlcNAc phosphotransferase so they didn't have a signal for lysosome degradation.