Characterization of a new member of the fatty acid-binding protein family that binds all-trans-retinol

Cellular retinol-binding protein, type I (CRBP-T) and type IT (CRBP-II) are the only members of the fatty acid-binding protein (FABP) family that proc ess intracellular retinol. Heart and skeletal muscle take up postprandial r etinol but express little or no CRBP-I or CRBP-II. We have identified an in tracellular retinol-binding protein in these tissues. The 134-amino acid pr otein is encoded by a cDNA that is expressed primarily in heart, muscle and adipose tissue. It shares 57 and 56% sequence identity with CRBP-I and CRB P-II, respectively, but less than 40% with other members of the FABP family , In situ hybridization demonstrates that the protein is expressed at least as early as day 10 in developing heart and muscle tissue of the embryonic mouse. Fluorescence titrations of purified recombinant protein with retinol . isomers indicates binding to all-trans-, 13-cis-, and 9-cis-retinol, with respective K-d values of 109, 83, and 130 nM. Retinoic acids (all-trans-, 13-cis-, and 9-cis-), retinals (all-trans-, 13-cis-, and 9-cis-), fatty aci ds (laurate, myristate, palmitate, oleate, linoleate, arachidonate, and doc osahexanoate), or fatty alcohols (palmityl, petrosenlinyl, and ricinolenyl) fail to bind. The distinct tissue expression pattern and binding specifici ty suggest that we have identified a novel FABP family member, cellular ret inol-binding protein, type III.