Lipoprotein Assembly

Question 1

apoB

Answer 1

ApoB is the main protein on CM, VLDL, and LDL

Question 2

ApoB100 vs apoB48

Answer 2

ApoB100: stabilizes VLDL and LDL, produced in liver and present on VLDL and LDL
1. structural protein
2. LDL uptake, recognized by LDL receptor

ApoB48: N-terminal of ApoB100, 48% of ApoB100, cannot bind to LDL because it has no C-terminal, on VLDL/chylomicron remnants is recognized by the remnant
1. Structural protein
2. not recognized by LDL receptor

Question 3

How is ApoB48 produced

Answer 3

Transcribed from the same gene as apoB100, but under goes RNA editing in the intestine

Question 4

Where are Cm/VLDL assembled? structures of CM,VLDL,LDL

Answer 4

CM in intestine
VLDL in liver

CM/VLDL:
* Particles composed of a TG-rich core with a small content of CE, a surface monolayer of phospholipid and cholesterol and
apolipoproteins
* Although CM and VLDL are produced by different tissues, the
process is similar

LDL: Produced in circulation from VLDL, CE-rich core

Question 5

5 steps

model of VLDL/CM assembly? does it require co-translational or post-translational lipidation?

Answer 5

Required co-translation and post-translational lipidation
1. Generation of lumenal lipid droplets
2.Translation/ translocation of apoB into ER lumen
* Co-translational addition of lipids to apoB –> nascent CM/VLDL
3. Post-translational addition of lipids (fusion) to nascent CM/VLDL –> mature CM/VLDL
* apoB is fully translocated
4. Secretion into circulation
5. Addition of other apolipoproteins (apoE, apoCII) occurs in the circulation

Question 6

What protein is needed for VLDL/CM assembly

Answer 6

MTP
Facilitates the formation of CM/CLDL by catalyzing the transfer of TG and PL

Question 7

Abetalipoproteinemia (description, mutation in what protein, symptoms, treatment)

Answer 7

Genetic disease of lipoprotein assembly (CM/CLDL)

Mutation in MTP

absence of apoB-containing plasma lipoproteins (CM, VLDL, and LDL)
low concentration of TG and cholesterol in blood

Failure to grow in infancy
fatty stools
loss of vision
vitamin E deficiency

Low fat diet, vitamin E supplement

Question 8

MTP inhibitor

Answer 8

Cholesterol is reduced, has some toxic effects
Increased ALT indicates liver damage
also caused fatty liver

Question 9

What does increased ALT indicate

Answer 9

Indicates liver damage

Question 10

MTP function

Answer 10

Facilitates the formation of CM/CLDL by catalyzing the transfer of TG and PL