Bacterially produced apolipoprotein D binds progesterone and arachidonic acid, but not bilirubin or E-3M2H

Apolipoprotein D (ApoD) constitutes an atypical lipoprotein in so far as it is predominantly found associated with HDL particles but belongs to the lipocalin structural family. Apart from its involvement in serum lipid transport it is abundant in various tissues, and differing physiological functions have been ascribed to it. We have now developed an E. coli expression system that permits the efficient production of biochemically homogeneous ApoD via secretion into the bacterial periplasm. Detailed ligand binding studies by fluorescence titration revealed that progesterone and arachidonic acid are complexed with dissociation constants both in the 1 µM range, whereas the presumed ligands pregnenolone, bilirubin and E‐3M2H are not recognized by the recombinant protein. In contrast with previous reports it thus appears that ApoD discriminates well in its binding function between closely related compounds. Copyright © 2001 John Wiley & Sons, Ltd. Abbreviations used: ANS 8‐anilino‐1‐naphthalenesulfonic acid ApoD apolipoprotein D ASOB2 apocrine secretion odor‐binding protein 2 BBP bilin‐binding protein DMF N,N‐dimethylformamide E‐3M2H E‐3‐methyl‐2‐hexenoic acid GCDFP‐24 gross cystic disease fluid protein 24 HDL high density lipoprotein KD dissociation constant OmpA outer membrane protein A PBCP progesterone‐binding cyst protein PCR polymerase chain reaction RBP human serum retinol‐binding protein.