Apolipoprotein D, vertebrates (IPR026222)

Short name: ApoD_vertbrte

Family relationships


Apolipoprotein D (apoD) is a mammalian plasma lipoprotein first isolated in 1973 [PMID: 4128506]. Although well characterised, its precise biological function remains unclear. It has long been known that the majority of apoD constitutes a minor but significant protein component of high density lipoprotein particles (HDLs), representing about 5% of total HDL protein, and that its interaction with other apolipoproteins is of considerable importance [PMID: 6774335, PMID: 6789837].

By contrast with most apolipoproteins, human apoD is relatively small: sequencing studies [PMID: 3453108] have indicated a translation product of 189 residues with a calculated MW of approximately 18500. ApoD is 18% glycosylated, at either or both of two asparagines (positions 65 and 98 [PMID: 3453108]), giving an overall MW of 29,000-32,000 [PMID: 6789837, PMID: 3711120]. Isoelectric focusing of human apoD shows 3 bands with pI 5.20, 5.08 and 5.00, with a minor band at pI 4.7 [PMID: 6789837]. By contrast, rat apoD shows a heterogeneous pI in the range 4.05 to 4.37 [PMID: 2090718].

Human apoD is distributed widely: its mRNA has been detected in a number of tissues, including kidney, liver, pancreas, spleen, intestine, placenta, adrenal gland and foetal brain tissue [PMID: 2439269]. The tissue distribution in the rat resembles that of human apoD, except that its plasma concentration is low [PMID: 2120218]. More recently, the large scale expression of apoD has been identified in regenerating peripheral nerve tissue [PMID: 2090718, PMID: 1695148].

There is some evidence that the expression of apoD is regulated by steroid hormones [PMID: 1868457]. The tissue distribution of apoD is quite different from that of other apolipoproteins; only the liver and intestines are significant shared sites of synthesis. ApoD is found in a number of mammalian species, including humans and other primates (such as baboons, rhesus and cynomalgas monkeys), rats, rabbits and goat, but it is absent from pig, dog, cow and horse.

The complete sequences of human, rat and rabbit apoD have been determined: the gene sequences are of similar length and are well conserved. Analysis of the human sequence revealed that apoD is a lipocalin family member showing the greatest apparent similarity to insect coloura.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.