Glycoslation

Question 1

what are the types of post-trans mod?

Answer 1

glycosylation, phosphorylation, ubiquitylation, SUMOylation

Question 2

what is glycoengineering?

Answer 2

“playing” with the type and site of glycosylation to potentiate biological activity

Question 3

what are the classes of glycos?

Answer 3

N-linked (Asn); O-linked (Ser, Thr); Phosphoglycans (found on Ser/Thr rich motifs); C-linked glycans (rare; sugar added to a C on a Trp side chain); Glypiation (addition of glycosylphosphatidylinositol, GPI, membrane anchor)

Question 4

roles o N-linked glycos?

Answer 4

structural and or functional roles, such as cell-cell adhesion; also, promotes stability and proper folding–probably why it is covalently attached?

Question 5

where ar ethe protein that undergo N-linked glycos synthesized?

Answer 5

primarily in RER

Question 6

what is the function of Ost>

Answer 6

scans nascent protein as it emerges from translocon in ER; recognizes Asn-X-Ser/Thr and transfers a glycan consisting of 3 glucose, 9 mannose, and 2 N-Acetylglucosamine

Question 7

what is the significance of glucose removal form the 14-sugar glycan on protein?

Answer 7

when the protein has folded, and with the glucose gone, it will be allowed to leave the ER

Question 8

what targets a protien to the lysosome?

Answer 8

addition of mannose-6-phosphate; inability to do so frequently results in lysosomal deficiencies

Question 9

most EC proteins have alpha3 and 6 mannose substitued with N-Ac glc

Answer 9

ya

Question 10

variation of glycos is important in the interaction between microorganism and host

Answer 10

ya

Question 11

glycosyl transferases general info

Answer 11

act sequentially to produce an array of glycans; require divalent cation as catalytic cofactr; most active bw pH 5-7 (ER-golig-plasmalemma pathway)

Question 12

glycotransferases and glycosidases are competing enzymes–regulate structure/composition of a glycan

Answer 12

ya

Question 13

how is glycosylation determined?

Answer 13

compartmentalization; seq of amino acid has a small role to play, but final compartment matters more

Question 14

every compartment has a different amount of glucosidases and glycotransferases

Answer 14

ya

Question 15

compare and contrast N vs O-linked glycosylation

Answer 15

N happens co-translationally, while O happens post; N has an en bloc transfer (transfers all at once) while for O the glycosyl molecule is build onto the protein; N-linked happens on Asn while O happens on Ser or Thr; dolichol phosphate is required for N but not O; modifying enzymes are soluble in N but O they are membrane bound; N happens in ER and golgi while O is just golgi

Question 16

Addition of the 14-sugar oligo occurs in ER for N-linked; requires 15 Asn Linked Glycosylation genes; first two steps are cytosolic–>precursor built on a DP backbone

Answer 16

ya

Question 17

modification of N-linked glycosyl happens in ER–>removal of glucose to give high mannose

Answer 17

ya

Question 18

extensive mods of teh glycans happen in the golgi–> e.g. addition of mannose-6-phosphate, which targets protein to lysosome

Answer 18

ya