InterPro domain: IPR000566

Proteins which transport small hydrophobic molecules such as steroids, bilins, retinoids, and lipids share limitedregions of sequence homology and a common tertiary structure architecture [ 1 , 2 , 3 , 4 , 5 ]. This is an eight stranded antiparallel beta-barrel with a repeated + 1 topology enclosinga internal ligand binding site [ 6 , 6 ]. The name 'lipocalin' has been proposed [ 6 ] forthis protein family, but cytosolic fatty-acid binding proteins are also included. The sequences of most members of the family, the core or kernal lipocalins, are characterised bythree short conserved stretches of residues, while others, the outlier lipocalin group, share only one or two of these[ 6 , 7 ]. Proteins known to belong to this family include alpha-1-microglobulin (protein HC);alpha-1-acid glycoprotein (orosomucoid) [ 7 ]; aphrodisin; apolipoprotein D; beta-lactoglobulin; complementcomponent C8 gamma chain [ 8 ]; crustacyanin [ 9 ]; epididymal-retinoic acid binding protein(E-RABP) [ 10 ]; insectacyanin; odorant-binding protein (OBP); human pregnancy-associated endometrial alpha-2globulin; probasin (PB), a rat prostatic protein; prostaglandin D synthase ( 5.3.99.2 ) [ 11 ]; purpurin; VonEbner's gland protein (VEGP) [ 12 ]; and lizard epididymal secretory protein IV (LESP IV) [ 13 ].

1. Homology and structure-function correlations between alpha 1-acid glycoprotein and serum retinol-binding protein and its relatives. FASEB J. 1, 209-14
2. Structural organization of the gene for prostaglandin D synthase in the rat brain. Proc. Natl. Acad. Sci. U.S.A. 89, 5376-80
3. Crystallographic refinement of human serum retinol binding protein at 2A resolution. Proteins 8, 44-61
4. Structure and sequence relationships in the lipocalins and related proteins. Protein Sci. 2, 753-61
5. The structural motif of beta-lactoglobulin and retinol-binding protein: a basic framework for binding and transport of small hydrophobic molecules? Trends Biochem. Sci. 13, 64-6
6. Mouse oncogene protein 24p3 is a member of the lipocalin protein family. Biochem. Biophys. Res. Commun. 180, 69-74
7. Drug binding to human alpha-1-acid glycoprotein in health and disease. Pharmacol. Rev. 40, 1-47
8. Structural and functional characterization of complement C8 gamma, a member of the lipocalin protein family. Mol. Immunol. 28, 123-31
9. Complete sequence and model for the A2 subunit of the carotenoid pigment complex, crustacyanin. Eur. J. Biochem. 197, 407-17
10. Structure of the epididymal retinoic acid binding protein at 2.1 A resolution. Structure 1, 7-18
11. The first lipocalin with enzymatic activity. Trends Biochem. Sci. 16, 363
12. Structural organization of the genes for rat von Ebner's gland proteins 1 and 2 reveals their close relationship to lipocalins. Eur. J. Biochem. 221, 905-16
13. LESP, an androgen-regulated lizard epididymal secretory protein family identified as a new member of the lipocalin superfamily. J. Biol. Chem. 268, 10274-81