Week 2

Question 1

FLIPPASE

Answer 1

• P1-5
• ATPase
• OUT to IN
• PE & PS
• P4ATPase + CDC
• ATP required
• ## Actuator, Phosphorylation, nucleotide binding

Question 2

Floppase

Answer 2

• ABCB1
• IN to OUT
• Requires ATP
  MECHANISM
• binding of lipid to tranporter
• cytoplasmic side binding and hydrolysis
• ADP released and new ATP binds to secondary ATP-binding site
• hydrolysis and release of ADP and a phosphate molecule resets the protein

SUBSTRATES
- PC
- sphingomyelin
- lysophospholipids
- HDL

Question 3

Scramblases

Answer 3

• energy independant
• bidirectional

TMEM16
- scarmbling domain IV & V
- Ca2+ binding TM VI-VIII
- can act as cation channels

Mechanism with flippase
- high Ca2+ increase TMEM16F
- inactivcates P4-ATPase
- when Ca2+ returns normal
- TMEM16F stops scrambling
- constant slipping of PS prevents PS-exposing cells to be engulfed by macrophages

Question 4

8 steps of lipid transfer

Answer 4

• Donor membrane docking
• Lipid extraction
• Donor membrane undocking
• Diffusion
• Acceptor membrane docking
• Lipid deposition
• Acceptor membrane undocking
• Further diffusion

Question 5

TULIP

Answer 5

• create cavities or channels that accommodate the hydrophobic tails of lipids, facilitating lipid transport
• spinny thing

Question 6

A. Anchoring to the outside

Answer 6

GPI modification
Anchors protein to outer leaflet
Stable
Flexible leash
Essential for protein to remain attached to the cell
Specific phospholipase can release protein in response to signals
PrPc: prion protein associated with BSE (bovine spongiform encephalopathy)
Mad cow disease – when defective

Question 7

B1.N-terminal myristoylation

Answer 7

Added to N-terminus
N-myristoyltransferase
Removes methionine
Transfers C14 myristate fatty acid from it carrier coenxyme A to the new N-terminal glycine residue
Consensus – MGxxxStKrKr – consensus strand is a common sequence found for process
Forms strong amide bond
Can not be removed unless cleaved
e.g. Src Kinase
o Sarcoma
o Tyrosine kinase; activated by EGFR

Question 8

B2. Palmitoylation of cysteine residues

Answer 8

Added post-transcriptionally
Reversible
Consensus not well defined
Enzyme: palmitoyltransferase
e.g. – Ras

Question 9

B3 a. Farnesylation

Answer 9

Post-transcriptional, thioether linkage of farnesyl (C15) group
* Enzyme-linked (farnesyl transferase)
* Stable
* Consensus motif:
CaaXcooh (a: aliphatic, X:M,S,C,Q preferred)
After modification aaX residues removed, and new cooh methylated
Example: GTP Ras (activated ERK signalling pathway)

Question 10

B3 b. Geranylgeranylation

Answer 10

Post-translation, thioether linkage of geranylgeranyl (C20) group
Enzyme-linked (geranylgeranyl transferase I and II)
Stable
Consensus motifs
For GGT I: CaaXcooh
For GGT II enzyme: CCcooh, CXCcooh, CCXXcooh
Processed after modification as for faresykaton , above
Example: GTPase RhoA (Ras homolog family member A – controls local actin assembly)