Glycosylation 1 Flashcards
How is a hexane formed?
Hydroxyl group reacts with an aldehyde group to form a sugar ring
In a beta glucose is the hydroxyl group projected up or down on carbon 1?
up
In a alpha glucose is the hydroxyl group projected up or down on carbon 1?
down
What is a epimer?
Differ from glucose by one chiral position.
All derived from glucose
What does epimerisation at c4 of glucose form?
Galactose
Addition of amino acid group to D-galactose forms what?
GalNAC
What is sialic acid?
The name for N-acetylneuraminic acid (NeuAc)
Are sugar monomers added as precursors?
Glycosidic bond formation is not spontaneous (energetically favourable) hence activated monomers are used
What are sugar monomer precursors activated with ?
UDP- sugar
energy provided by two ATPs consumed to form UDP-sugar
What residue are N-linked glycans built on?
asparagine
What is yeast N-linked glycosylation pattern like?
High mannose sugar
What is Insects N-linked glycosylation pattern like?
Low amounts of mannose
What is Plants N-linked glycosylation pattern like?
Complex sugars
Similar to humans but have additional xylose
What is mammals N-linked glycosylation pattern like?
Similar to human
Some bisecting glcNAC when branching is not extended
What is human N-linked glycosylation pattern like?
Only main difference from mammalian sugars is that the terminal Salic is different by one hydroxyl
Which are longer, O-linked or N-linked?
O-linked
Can be used to push receptors above the fuzzy glycan layer
Name some intrinsic function of gylcans.
Providing structural components
Modifying protein properties (solubility, stability)
Name some extrinsic function of glycans.
Directing trafficking
mediating cell adhesion
mediating signalling
What is the affect of HIV proteins glycosylation by host cells?
Protein are recognised as self
What is special about alpha-L-iduronidase?
Uses its own N-glycan as a substrate binding and catalytic module
How does a peptide enter the lumen of the ER?
Threaded through the membrane into the lumen translationally
What is the oligosaccharide precursor built on?
dolichol
How many mannoses are removed in the ER?
1
How many mannoses are the sugars trimmed back to in the golgi?
5
Describe the dolichol.
phospholipid with large with large isoprene
How does flippase work?
not known
Additions of N-linked sugars are co or post translational?
Co-translational
Describe the quality control pathway in the ER?
Proteins enter the ER with 3 Glucoses. This is trimmed back to 1 so the protein can be recognized by calnexin.
Glucosidase cleaves the last glucose.
If normally folded it leaves the ER.
If incorrectly foled it binds a chaperone and a glucose is readded and it re-cycles.
Removed for degradation if has spent to long in ER and mannosidase has removed a mannoses.
What is the specificity of PNGase?
Cuts between Asn and first sugar
What is the main method of glycan analysis?
MALDI mass spec
How would you determine glycan structure in a mixture of glycans?
Sequentially add enzymes that target different end sugars and note which peaks move until they share one singular peak i.e. main chain is the same
What is the specificity of EndoH?
Cuts between first and second sugar of high mannose glycans
Why can EndoH be used to distinguish between secreted and non-secreted protein?
high mannose normally means not secreted
The sugars are primarily stereoisomers and will have the same mass. How do you distinguish between them in a mass spec?
By prior knowledge to assign peaks
NMR can be used to give 3D structures of glycans. True or false?
true
