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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/05/12 19:56:49」(JST)

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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.

Functions

In lipid transport, apolipoproteins function as structural components of lipoprotein particles, cofactors for enzymes and ligands for cell-surface receptors. In particular, apoA1 is the major protein component of high-density lipoproteins; apoA4 is thought to act primarily in intestinal lipid absorption. Further, apoE is a blood plasma protein that mediates the transport and uptake of cholesterol and lipid by way of its high affinity interaction with different cellular receptors, including the low-density lipoprotein (LDL) receptor. Recent findings with apoA1 and apoE suggest that the tertiary structures of these two members of the human exchangeable apolipoprotein gene family are related.^[1] The three-dimensional structure of the LDL receptor-binding domain of apoE indicates that the protein forms an unusually elongated four-helix bundle that may be stabilised by a tightly packed hydrophobic core that includes leucine zipper-type interactions and by numerous salt bridges on the mostly charged surface. Basic amino acids important for LDL receptor binding are clustered into a surface patch on one long helix.^[2]

They are enzyme coenzymes (C-II for lipoprotein lipase and A-I for lecithin-cholesterol acyltransferase)
Lipid transport proteins
Ligands for interaction with lipoprotein receptors in tissues ( apoB100 and apoE for LDL-receptors, apoA-I for HDL receptors)

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. 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 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 ancestral gene. 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.

Synthesis and regulation

Apolipoprotein synthesis in the intestine is regulated principally by the fat content of the diet.

Apolipoprotein synthesis in the liver is controlled by a host of factors, including dietary composition, hormones (insulin, glucagon, thyroxin, estrogens, androgens), alcohol intake, and various drugs (statins, niacin, and fibric acids). Apo B is an integral apoprotein whereas the others are peripheral apoproteins.

References

^ Saito H, Lund-Katz S, Phillips MC (July 2004). "Contributions of domain structure and lipid interaction to the functionality of exchangeable human apolipoproteins". Prog. Lipid Res. 43 (4): 350–80. doi:10.1016/j.plipres.2004.05.002. PMID 15234552.
^ Wilson C, Wardell MR, Weisgraber KH, Mahley RW, Agard DA; Wardell; Weisgraber; Mahley; Agard (June 1991). "Three-dimensional structure of the LDL receptor-binding domain of human apolipoprotein E". Science 252 (5014): 1817–22. Bibcode:1991Sci...252.1817W. doi:10.1126/science.2063194. PMID 2063194.
^ Fullerton SM, Buchanan AV, Sonpar VA, Taylor SL, Smith JD, Carlson CS, Salomaa V, StengÃ¥rd JH, Boerwinkle E, Clark AG, Nickerson DA, Weiss KM (June 2004). "The effects of scale: variation in the APOA1/C3/A4/A5 gene cluster". Hum. Genet. 115 (1): 36–56. doi:10.1007/s00439-004-1106-x. PMID 15108119.

External links

HuGENet Review
Apolipoprotein AI Mutations and Information

This article incorporates text from the public domain Pfam and InterPro IPR000074

UpToDate Contents

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English Journal

Carbamylation of LDL and its relationship with myeloperoxidase in type 2 diabetes mellitus.

Shiu SW, Xiao SM, Wong Y, Chow WS, Lam KS, Tan KC.Source*Department of Medicine, University of Hong Kong, Hong Kong.
Clinical science (London, England : 1979).Clin Sci (Lond).2014 Jan;126(2):175-81. doi: 10.1042/CS20130369.
LDL (low-density lipoprotein) is subjected to pro-atherogenic modifications in the circulation. A novel uraemia-independent mechanism of carbamylation of lipoproteins mediated by MPO (myeloperoxidase) has recently been reported. We have investigated whether carbamylation of LDL was increased in pati
PMID 23905837

Cognitive impairment in neurological diseases: lessons from apolipoprotein e.

Shi J, Han P, Kuniyoshi SM.SourceDepartment of Neurology, Barrow Neurological Institute, Phoenix, AZ, USA.
Journal of Alzheimer's disease : JAD.J Alzheimers Dis.2014 Jan 1;38(1):1-9. doi: 10.3233/JAD-130623.
Apolipoprotein E4 (ApoE4) has been considered to have detrimental effects on the age of onset and progression in Alzheimer's disease. Evidence continues to accumulate regarding the effects of ApoE isoforms in a number of other neurological diseases. Recent studies demonstrate an increase in cognitiv
PMID 23948926

Excess nitric oxide impairs LXR(α)-ABCA1-dependent cholesterol efflux in macrophage foam cells.

Zhao JF, Shyue SK, Lin SJ, Wei J, Lee TS.SourceDepartment of Physiology, National Yang-Ming University, Taipei, Taiwan.
Journal of cellular physiology.J Cell Physiol.2014 Jan;229(1):117-25. doi: 10.1002/jcp.24429.
Excess nitric oxide (NO) promotes the progression of atherosclerosis by increasing the oxidation of low-density lipoprotein (LDL) and inflammatory responses. However, little is known about the impact of NO and its underlying molecular mechanism on lipid metabolism of macrophage foam cells. In this s
PMID 23836449

Japanese Journal

Increases in Plasma Aβ40 Levels and the Aβ40/42 Ratio in Patients with Diabetes Mellitus and Dementia

弘前医学 66(2-4), 110-119, 2016-03-25
NAID 120005728504

Serum Apolipoprotein M Levels are Correlated with Biomarkers of Coagulation

The Kitakanto medical journal = 北関東医学 66(1), 1-6, 2016-02
NAID 120005723273

リポタンパク関連臨床指標の進歩と課題 (代謝) -- (臨床分野での進歩)

Annual review. 糖尿病・代謝・内分泌, 126-135, 2016
NAID 40020739719

Related Pictures

★リンクテーブル★

リンク元	「アポリポタンパク」「アポリポ蛋白」「アポリポ蛋白質」「アポリポタンパク質」「apo」
拡張検索	「apolipoprotein A-I」「apolipoprotein A2」
関連記事	「apolipoproteins」

「アポリポタンパク」

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

Apolipoprotein
	apolipoprotein e3 (apoe3)
Identifiers
Symbol	Apolipoprotein
Pfam	PF01442
InterPro	IPR000074
SCOP	1oef
SUPERFAMILY	1oef
OPM superfamily	193
OPM protein	3r2p
Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary