Crystallization and preliminary X-ray study of two liver basic fatty acid-binding proteins

The fatty acid-binding proteins (FABPs) are a very well known protein famil y which includes the liver basic FABPs (Lb-FABPs), a subgroup so far charac terized in several vertebrates but not in mammals. The most important diffe rence recognized between the proteins in this subgroup and the better known mammalian liver FABPs (L-FABPs) is the stoichiometry of ligand binding: tw o fatty acid molecules in L-FABPs compared with one in Lb-FABPs. The only L b-FABP with a known three-dimensional structure is that of chicken Lb-FABP, but the details of ligand binding are still unresolved as the crystals of the protein are grown at an acidic pH and the protein has been shown to los e its ligand under these conditions. The two proteins whose crystallization s are reported here are the second and third members of this subfamily to b e crystallized. The crystals of axolotl Lb-FABP belong to either space grou p P4(1)2(1)2 or P4(3)2(1)2, with unit-cell parameters a=b=65.38, c=60.90 An gstrom, and diffract to a resolution of 2.0 Angstrom on a conventional sour ce at room temperature. The crystals of toad Lb-FABP belong to either space group P4(1)22 or P4(3)22, with unit-cell parameters a=b=48.14, c=135.23 An gstrom, and diffract to 2.5 Angstrom resolution under the same conditions. It is expected that the solution of these two structures will help to clari fy the structural differences between Lb-FABPs and L-FABPs and will possibl y explain the different binding stoichiometries observed in these otherwise so similar protein subfamilies.