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Publication Abstract from PubMed

Human apolipoprotein D (ApoD) occurs in plasma associated with high density lipoprotein. Apart from the involvement in lipid metabolism, its binding activity for progesterone and arachidonic acid plays a role in cancer development and neurological diseases. The crystal structures of free ApoD and its complex with progesterone were determined at 1.8A resolution and reveal a lipocalin fold. The narrow, mainly uncharged pocket within the typical beta-barrel accommodates progesterone with its acetyl side chain oriented toward the bottom. The cavity adopts essentially the same shape in the absence of progesterone and allows complexation of arachidonic acid as another cognate ligand. Three of the four extended loops at the open end of the beta-barrel expose hydrophobic side chains, which is an unusual feature for lipocalins and probably effects association with the high density lipoprotein particle by mediating insertion into the lipid phase. This mechanism is in line with an unpaired Cys residue in the same surface region that can form a disulfide cross-link with apolipoprotein A-II.

Structural insight into the dual ligand specificity and mode of high density lipoprotein association of apolipoprotein D.,Eichinger A, Nasreen A, Kim HJ, Skerra A J Biol Chem. 2007 Oct 19;282(42):31068-75. Epub 2007 Aug 14. PMID:17699160^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.