Lipocalin, ApoD type (IPR022271)

Short name: Lipocalin_ApoD

Family relationships


The lipocalins are a diverse, interesting, yet poorly understood family of proteins composed, in the main, of extracellular ligand-binding proteins displaying high specificity for small hydrophobic molecules [PMID: 2580349]. Functions of these proteins include transport of nutrients, control of cell regulation, pheromone transport, cryptic colouration, and the enzymatic synthesis of prostaglandins.

The crystal structures of several lipocalins have been solved and show a novel 8-stranded anti-parallel beta-barrel fold well conserved within the family. Sequence similarity within the family is at a much lower level and would seem to be restricted to conserved disulphides and 3 motifs, which form a juxtaposed cluster that may act as a common cell surface receptor site [PMID: 1834059, PMID: 7684291]. By contrast, at the more variable end of the fold are found an internal ligand binding site and a putative surface for the formation of macromolecular complexes [PMID: 8573354]. The anti-parallel beta-barrel fold is also exploited by the fatty acid-binding proteins, which function similarly by binding small hydrophobic molecules. Similarity at the sequence level, however, is less obvious, being confined to a single short N-terminal motif.

This entry represents ApoD type Lipocalin, including Retinol-binding protein 4 as well as other retinol-binding proteins. Apolipoprotein D (ApoD) occurs in the macromolecular complex and is involved in lecithin-transport and binding of bilin. It appears to be able to transport a variety of ligands in a number of different contexts.

Contributing signatures

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