Apolipoprotein

As apolipoproteins ( apo- from the Greek άπό: From, path ) refers to the protein moiety of the lipoproteins (eg chylomicrons, VLDL, LDL, IDL, HDL), which transports the water-insoluble lipids in the blood. The apolipoproteins together with phospholipids, the water-soluble (hydrophilic ) surface of lipoproteins, where they act as a structural scaffold and / or detection and Andockmolekül eg for membrane receptors.

Building, structure, function

Since the apolipoproteins with the exception of ApoBs can switch back and forth between individual lipoprotein particles, the combination of the different apolipoproteins changes on a lipoprotein progresses metabolism in the bloodstream. Apolipoprotein composition indicates the composition of the actual lipid and lipoprotein directs it into the next phase of its pathway until it is finally taken up into a cell in the body, in most cases, a liver cell.

Apolipoproteins are produced in the tissues synthesize the lipoproteins, that is, particularly in the liver and in the small intestine. The names of the apolipoproteins are historical ( ApoAs were first in HDL, LDL and ApoBs in their precursors and ApoCs in VLDL found ) and was generally of a capital letter and possibly a trailing number, together. The following table contains information on some of the known major apolipoproteins.

Structurally similar to apoA and apoC proteins and ApoE, as they contain many repeating amphipathic α -helices that exist at the genetic level of tandem repeats of 11 codons and are therefore very likely evolved from a Ursprungsgen. Interestingly, these genes are located in two gene clusters distributed in the human genome close to each other: ApoC-I/-II/-IV/ApoE on chromosome 19q3.2 - Q3.3 and ApoA-I/-IV/-V/ApoC-III on chromosome 11q23 - q24. In contrast, the two apoB proteins are transcribed from a single gene ( ApoB -48 is produced by RNA editing - in humans only in the small intestinal epithelium ) and consist mainly of extended amphipathic β -sheet structures, probably the for the strong association with are lipid core charge.

A number of disorders of lipid metabolism can be due to defects of production of apolipoproteins or the docking of the cell wall (e.g., the LDL receptor ). The measurement of blood levels of the various apolipoproteins is part of the diagnosis of these diseases, their clinical relevance is therefore high especially because a defective metabolism of fat usually has an influence on the risk of arteriosclerosis and thus on the life expectancy of the patient.

ApoA -I ( M), a genetic variant of apoA -I, the so-called type Milano is currently being investigated to determine whether it is suitable as a therapeutic agent for atherosclerosis, since the carrier of this feature, the Milan fat researcher Cesare Sirtori in place Limone sul Garda found on Lake Garda, are characterized by long life and low level of atherosclerosis. Contrary to the usual fact that a high HDL is a protective factor against atherosclerosis, the carrier of the ApoA-I (M) have low HDL levels. ApoA-I (M) is to dimerize by an amino acid substitution in a position thus has a longer plasma half-life, may be more efficient to mobilize cholesterol and probably leads to a reduction in this way, of atherosclerotic plaques.