LIPOPROTEIN DISORDERS

Apolipoprotein

Apolipoproteins are proteins that bind lipids (oil-soluble substances such as fat and cholesterol) to form lipoproteins. They transport

the lipids through the lymphatic and circulatory systems.

The lipid components of lipoproteins are insoluble in water. However, because of their detergent-like (amphipathic) properties,

apolipoproteins and other amphipathic molecules (such as phospholipids) can surround the lipids, creating the lipoprotein particle that

is itself water-soluble, and can thus be carried through water-based circulation (i.e., blood, lymph).

Apolipoproteins also serve as enzyme cofactors, receptor ligands, and lipid transfer carriers that regulate the metabolism of

lipoproteins and their uptake in tissues.

Classes

There are two major types of apolipoproteins. Apolipoproteins B form low-density lipoprotein ("bad cholesterol") particles. These proteins

have mostly beta-sheet structure and associate with lipid droplets irreversibly. Most of the other apolipoproteins form high-density

lipoprotein ("good cholesterol") particles. These proteins consist of alpha-helices and associate with lipid droplets reversibly. During

binding to the lipid particles these proteins change their three-dimensional structure. There are also intermediate-density

lipoproteins formed by Apolipoprotein E.

There are six classes of apolipoproteins and several sub-classes:

•A (apo A-I, apo A-II, apo A-IV, and apo A-V)

•B (apo B48 and apo B100)

•C (apo C-I, apo C-II, apo C-III, and apo C-IV)

•D

•E

•H

Exchangeable apolipoproteins (apoA, apoC and apoE) have the same genomic structure and are members of a multi-gene family that

probably evolved from a common ancestralgene. ApoA1 and ApoA4 are part of the APOA1/C3/A4/A5 gene cluster on chromosome 11.[3]

Hundreds of genetic polymorphisms of the apolipoproteins have been described, and many of them alter their structure and function.

Lipoprotein lipase (LPL) (EC 3.1.1.34) is a member of

the lipase gene family, which includes pancreatic

lipase, hepatic lipase, and endothelial lipase. It is a water-

soluble enzyme that hydrolyzes triglycerides in lipoproteins,

such as those found in chylomicrons and very low-density

lipoproteins (VLDL), into two free fatty acids and

one monoacylglycerol molecule. It is also involved in

promoting the cellular uptake of chylomicron remnants,

cholesterol-rich lipoproteins, and free fatty acids.[1][2][3] LPL requires ApoC-II as a cofactor

PHOSPHOLIPIDS DISORDERS

CHOLESTEROL DISORDERS

TRIGLYCERIDES DISORDERS

KETON BODIES DISORDERS