CRYSTALLOGRAPHIC STUDIES ON A FAMILY OF CELLULAR LIPOPHILIC TRANSPORT PROTEINS - REFINEMENT OF P2 MYELIN PROTEIN AND THE STRUCTURE DETERMINATION AND REFINEMENT OF CELLULAR RETINOL-BINDING PROTEIN IN COMPLEX WITH ALL-TRANS-RETINOL

P2 myelin protein (P2) and cellular retinol binding protein (CRBP) are members of a family of cellular lipophilic transport proteins. P2 has been refined at a resolution of 2.7 Å, and CRBP has been solved by molecular replacement and refined to a resolution of 2.1 Å. The members of this family form a compact three-dimensional structure built up from ten anti-parallel strands that fold to form an orthogonal barrel containing the ligand. In P2, the carboxylate group of an oleic acid ligand interacts with the side-chains of two arginine (106 and 126), and one tyrosine (128) residues. The ligand adopts a U-shaped conformation. In CRBP, the all-trans-retinol has a planar conformation with its alcohol group hydrogen bonding to the side-chain of glutamine 108 (equivalent to residue 106 in P2). The local interactions of glutamine 108 explain CRBP's preference for binding retinol rather than retinal. The side-chain of lysine 40 makes a close contact with the isoprene tail of the retinol. © 1993 Academic Press, Inc.