Glycosylation and lipidation

Question 1

Glycans

Answer 1

• covalent, extra-proteinous modifications
• structural/modulatory roles
• diversity of monosaccharides
• produced by Gas

Question 2

GTs

Answer 2

either use
- dolichol-phosphate precursors or
- oligosaccharide transferases

Question 3

monosaccharide activation

Answer 3

• nucleotide sugars are linked to anomeric carbon via O-glycosidic bond
• releases monophosphate sugar and phosphate group

Question 4

Monosaccharide GT donors

Answer 4

• nucleotide diphosphates

Question 5

Glycan transport

Answer 5

• monophosphate retrograde antiporters
• lumen flippases

Question 6

N-glycosylation

Answer 6

• on Asn nitrogen side-chain
• targets secreted TM/EC domains
• transferred in sequons

Question 7

cis-Golgi

Answer 7

• 2x mannose trim
• 1x GlcNac add
• high mannose N glycans

Question 8

median Golgi

Answer 8

• 3x mannose trim
• 1x GlcNac addition
• 1x fucose addition
• 1x GlcNac addition

Question 9

trans Golgi

Answer 9

• 3x galactose addition
• 3x silica acid addition
• complex, heterogenous glycans

Question 10

N-glycosylation polymorphism in spike

Answer 10

• spike = 22 sequons
• stabilises RBD dynamics and recognition

Question 11

O-glycosylation

Answer 11

• on Ser/Thr et al.
• targets EC/cytoplasmic domains
• classified on 1st monosaccharide

Question 12

pro-hydroxylation

Answer 12

• prolyl hydroxylases
• collagen

Question 13

lys-hydroxylation

Answer 13

• Lysyl hydroxylases
• collagen

Question 14

tyr-hydroxylation

Answer 14

• glycogenin
• glycogen primer

Question 15

GalNac

Answer 15

• initiated in Golgi

Question 16

GalNac transferases

Answer 16

• approx 20 types
• generate 8 core glycans
• e.g. IgM1, IgG3 hinge regions, protease protection

Question 17

galactose O-glycosylation

Answer 17

• O-glycan polymorphism on glycophorin caused by different GT expression
• IgM recognises during blood transfusion

Question 18

mannose

Answer 18

• initiated in ER, completed in Golgi
• alpha-dystroglycan in muscle links exoskeleton to cytoskeleton

Question 19

arabinose

Answer 19

• on hydroxyproline in SPPP repeat
• extensins for cell wall expansion

Question 20

GPI

Answer 20

• catalysed by GPI transamidase

Question 21

GPI regulation

Answer 21

• lipid tail modification
• phospholipase C hydrolyses lipid double tail

Question 22

Example of GPI

Answer 22

• Matrix Metallo Proteases
• high in metastatic cancers

Question 23

Palmitoylation

Answer 23

• S-acylation on Cys residues
• O-acylation on Ser/Thr
• non consensus motif
• > 2000 proteins per cell
• catalysed by PATs
• palmitoyl-CoA substrate

Question 24

PATs

Answer 24

• 23 in mammals
• 23 in plants
• TM, catalytic DHHC motif
• enriched in Golgi

Question 25

Depalmitoylation

Answer 25

- acyl-protein thioesterases - multiple lipid tails per protein

Question 26

Palmitoylation function

Answer 26

cargo concentration at cisternal rim

Question 27

Myristoylation

Answer 27

- onto N-terminal glycine - NMTs - eukaryotic

Question 28

co-translational myristoylation

Answer 28

methionine aminopeptidase exposes N-terminal glycine

Question 29

post-translational myristoylation

Answer 29

caspase end-protease cleaves protein

Question 30

myristoylation example

Answer 30

- BID myristoylation

Question 31

Prenylation

Answer 31

- on Cys motif - C-terminal residue removal - -COOH methylated by cytoplasmic ER integral proteins