Functions Of Secreted Glycoproteins Flashcards
T or F: most extracellular Proteins are Glycoproteins
True
What are N-linked sugars attached to?
Asparagine (N)
What are O-linked sugars attached to?
Serine, Threonine, Hydroxylysine
T or F: Cells that are present in the wrong places in the body will likely die
True, e.g. liver cells can’t live in the skin
- This is due to lack of the appropriate receptors on the liver cell to get the stuff it needs from the environment
How does ebola initiate interactions with endothelial cells?
- Why not other cells?
- How does proliferation continue?
- Finds a coat glycoprotein on endothelial Cells
- Cell becomes infected and dies (Hemorrage)
- Soluble Glycoprotein blocks early general assault and inflammation (blocks neutrophils)
What is the difference between a glycoprotein and a proteoglycan?
**Note: that proteoglycans are just a subset of glycoprotein
Glycoprotein:
low amount of Carbs attached
Proteoglycan:
More sugar and GLYCOSAMINOGLYCAN chains (GAGs) are attached
What is a glycosaminoglycan (GAG)?
- Repeated polysaccharide with alternating amino sugars and acidic sugars
What is one important exception to the fact that all glycoproteins are extracellular and most extracellular proteins are glycosylated?
Albumin - abundant Serum Transport Protein
What are lectins?
Carbodydrate binding proteins for:
- cell attachment
- immune response
- lung surfactant
What glycoprotein is involved in copper binding and transport?
Ceruloplasmin
What is N-acetyl-glucosamine?
Glucose Ring Derivatized at the 2-position
T or F: Sialic acid is aka as N-Acetylneuraminate (NANA)
True
What is glycosylation?
- The process of transferring an oligosaccharide to a protein
****************************** N-linked Glycosylation: - Where does it occur? - When does it happen - How does it happen?
Where:
- Starts in Rough ER and is finished in the Golgi
When:
- AS the Polypeptide is being synthesized
How:
- Preassembled oligosaccharide is transferred to the appropriate Asparagine
What sequence gives consensus for N-linked glycosylation?
Asn-X-Ser/Thr
T or F: from yeast to man, the preassembled oligosaccharide is always the same
True
Dolichol:
- What is it?
- Bond Type?
- Predominant Sugar?
- Dolichol is a carrier of the universal pre-assembled oligosaccharide
- Linked to the Oligosaccharide via a diphosphate bond
- Mannose and Glucose are Predominant in this molecule
When can a preassembled oligosaccharide be transferred from Dolichol to another protein?
- Bonds Broken and Formed?
- Transferred to Asn-X-Ser/Thr
- Disulfate bond to Dolichol is broken, and N-glycosyl bond is formed
Where does Dolichol transfer the oligosaccharide to proteins, where is Dolichol located?
- Dolichol present in RER membrane transfers Oligosaccharide to and Asn In the RER LUMEN
If all N-glycolsylated proteins start off with the same oligosaccharide attached how do they differentiate?
- where does this occur
Remove:
- Glucoses
- Mannoses
Add:
- Galactose
- Sialic Acid
- Fructose
**Occurs as the protein passes from the ER to the Golgi
T or F: O-linked glycosylation occurs one sugar at a time
True
What adds glycosyl groups in O-linked glycosylation?
- substrate for these enzymes?
- Glycosyl Transferases Used
- Sugar Nucleotide (e.g. UDP-Gal) are used
What is the job of fibronectin?
- Binds Both Cells and Extracellular Matrix Molecules (e.g. Collagen)
What does the structure of fibronectin consist of?
- Dimer (2 similar subunits)
- Joined by Disulfide Bond at C-terminal
How many many Fibronectin Genes are there?
- How many isoforms
1 Gene
3 Isoforms
**Alternate splicing allows for this
What modules are in Fibronectin?
- Function
- Globular Polypeptides that are like beads on a string
- Each “Bead” has a different function
Module Functions:
- Cell (Integrin) Binding
- Collagen Binding
- Heparan Sulfate Binding
- Fibrin Binding
What is Laminin?
- Similar to Fibronectin (binds different things together) - formed in basal lamina
(glycoprotein)
What is aggrecan?
- Glycoprotein that forms a shock absorbing aggregate
What are 3 main functions of glycoproteins?
- Comprise Recognition Signals
- Intracellular Trafficking
- Building Protein-Protein Interactions for CT scaffolding
What happens if glycoproteins loose too many of their glycosylations?
- They loose their water solubility and fallout of solution
- PROTEASES then degrade these
T or F: glycosylation protects glycoproteins from degradation
True
What happens if 2 of the 10 sialic acids are removed from the glycosylated portion of ceruloplasmin?
Half Life Deceases by 700x
What is Beta-glycan?
Transmembrane glycoprotein:
- Hormone Receptor for transforming growth factor-beta
Integrins:
- What do they do?
- How do they do it?
What they do:
Transmembrane Glycoproteins that mediate Cell-matrix binding
How:
- Binding ECM protein to allow cells to grip a given surface
T or F: most cells must be anchored to ECM by integrin to be viable
True, keeping the cell bound to ECM keeps it in contact with cell survival signals
What is a cadherin?
Ca2+ dependent Adhesion Molecule
If you chop up liver and retina cells and mix them what will happen an why?
- Retina Cells will aggregate with each other and Liver cells will aggregate with other liver cells
- This happens because of specific Cell-Cell interactions that only occur between cells of the same type
What role do glycoproteins play in fertilization of an egg by sperm?
- Capacitation - sperm alters is membrane glycoprotein and gal-transferase recognizes egg
- Zona Pellucida (glycoproteins) act as a sperm receptor
What role do glycoproteins play in the extravasation of white cells?
- Selectins present on endothelial cells and bring white cells to a rolling stop
- Integrins then grab onto the cell tighter and it is pulled through the endothelium (extravasation)
**Leads to an inflammatory Response
Why would you want to inhibit selectin that is used in extravasation?
- Extravasation leads to inflammation
- After a heart attack inflammation is bad and can cause additional damage
**No selectin, then no extravasation
What is needed to target a protein to a Lysosome?
- Glycoprotein with a PHOSPHOMANNOSE
What happens if PHOSPHOMANNOSE can’t be added to a protein?
- It will not get targeted to lysosome
- This can cause accumulation of macromolecules in Lysosome
(e. g I-Cell disease and ß-glucuronidase)
T or F: sugars in glycoproteins are covalently attached
True
