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The crystal structure of the phosphoglycerate dehydrogenase from Escherichia coli is unique among dehydrogenases. It consists of three clearly separate domains connected by flexible hinges. The tetramer has approximate 222 symmetry with the principal contacts between the subunits forming between either the nucleotide binding domains or the regulatory domains. Two slightly different subunit conformations are present which vary only in the orientations of the domains. There is a hinge-like arrangement near the active site cleft and the serine effector site is provided by the regulatory domain of each of two subunits. Interdomain flexibility may play a key role in both catalysis and allosteric inhibition.

The crystal structure of the recombinant form of rat liver fatty acid-binding protein was completed to 2.3 Å and refined to an R factor of 19.0%. The structural solution was obtained by molecular replacement using superimposed polyalanine coordinates of six intracellular lipid-binding proteins as a search probe. The entire amino acid sequence of rat liver fatty acid-binding protein along with an amino-terminal formyl-methionine was modeled in the crystal structure. In addition, the crystal was obtained in the presence of oleic acid, and the initial electron density clearly showed two fatty acid molecules bound within a central cavity. The carboxylate of one fatty acid molecule interacts with arginine 122 and is shielded from free solvent. It has an overall bent conformation. The more solvent-exposed carboxylate of the other oleate is located near the helix-turnhelix that caps one end of the ␤-barrel, while the acyl chain lies in the interior. The cavity contains both polar and nonpolar residues but also shows extensive hydrophobic character around the nonpolar atoms of the ligands. The primary and secondary oleate binding sites appear to be totally interdependent, mainly because favorable hydrophobic interactions form between both aliphatic chains.

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