assembly of HDL Flashcards
what is an initial step involved in reverse cholesterol transport
The synthesis of preβ-HD
what are essential things for the synthesis of preβ-HD
ApoA-I and ABCA1
what is the major protein component of
HDL
ApoA-I
what are the functions of ApoA-I
– maintaining the structure of HDL
– interacting with lipid transporters (ABCA1)
– activating lecithin:cholesterol acyltransferase
(LCAT)
– antioxidant
what synthesizes and secretes ApoA-I
the liver and intestine
is ApoA-I exchangeable or not
it is
how many ApoA-I molecules can reside on chylomicrons and HDL
multiple
what is preβ-HDL, how does its density differ to mature HDL
- As its name suggests, it is a type of HDL
that has preβ-migrating properties (based
on electrostatic charge) - It is a very small form of HDL with a
density that is greater than ‘mature’ HDL
(or HDL 1-HDL4)
what is the percent mass of preβ-HDL
By percent mass, it is almost exclusively
protein than lipid
size of all the HDLs and preβ-HDL
going from 1-4 they get smaller and the smallest is preβ-HDL
they decrease in the number of apo-a-i going from 1-4 to preβ-HDL
they have less to no fat and CE going from 1-4 to preβ-HDL
what is cholesterol efflux
Cholesterol efflux is the transfer of
cholesterol (and phospholipid) from cells
to HDL
why is cholesterol efflux essential
Cholesterol efflux to apoA-I is essential for
generating preβ-HDL and ‘mature’ HDL
how is the efflux to apoA-I done
via ABCA1
what is another form of cholesterol efflux that occurs and via what
Cholesterol efflux to ‘mature’ HDL also
occurs, but it is not essential
– Efflux via ABCG1 and SR-BI
The conversion of nascent HDL to mature
HDL in the circulation requires
one key
enzyme and a “transfer protein”:
what is the one key enzyme and a transfer protein required for conversion of nascent HDL to mature HDL
– Lecithin:cholesterol acyl transferase (LCAT)
– Phospholipid transfer protein (PLTP)
what is a cofactor for LCAT activity
apoA-I
what provides phospholipids to HDL in the circulation
PLTP
what does PLTP do
PLTP transfers excess phospholipid from
apoB100-containing lipoproteins to HDL.
importance of PLTP
– Provides phospholipid to expand the HDL surface
area.
– Provides lecithin (or phosphatidylcholine) for LCAT
activity.
– Contributes to the metabolism of apoB100-containing
lipoproteins into LDL.
ABCG1 functions
- ABCG1 functions similarly to ABCA1
- ABCG1 effluxes cholesterol (and
phospholipid) to ‘mature’ HDL
SR-BI structure
SR-BI has both N- and C-terminal
transmembrane domains with the ends of
the protein exposed to the cytosol, while
the remainder is exposed to the circulation
where is SR-BI expressed
in most tissues
function of SR-BI
It has bidirectional function:
– In the liver it binds ‘mature’ HDL via its apoA-I
and brings cholesterol into the cells
(…selective uptake)
– In other tissues it binds ‘mature’ HDL via its
apoA-I and transfers cholesterol to HDL
(…cholesterol efflux)
what HDLs carry TGs
HDL 1, 2, 3
how do TGs get into HDL 1-3
In humans, the triglycerides come from
apoB-containing lipoproteins, in exchange
for cholesteryl esters from the HDL
* This transfer occurs in the bloodstream
through a transfer protein called
cholesteryl ester transfer protein (CETP)
