title: The crystal structure of YdcE, a 4-oxalocrotonate tautomerase homologue from Escherichia coli, confirms the structural basis for oligomer diversity.
abstract: The tautomerase superfamily consists of three major families represented by 4-oxalocrotonate tautomerase (4-OT), 5-(carboxymethyl)-2-hydroxymuconate isomerase (CHMI), and macrophage migration inhibitory factor (MIF). The members of this superfamily are structurally homologous proteins constructed from a simple beta-alpha-beta fold that share a key mechanistic feature; they use an amino-terminal proline, which has an unusually low pK(a), as the general base in a keto-enol tautomerization. Several new members of the 4-OT family have now been identified using PSI-BLAST and categorized into five subfamilies on the basis of multiple-sequence alignments and the conservation of key catalytic and structural residues. The members of subfamily 5, which includes a hypothetical protein designated YdcE from Escherichia coli, are predicted not to form hexamers. The crystal structure of YdcE has been determined to 1.35 A resolution and confirms that it is a dimer. In addition, YdcE complexed with (E)-2-fluoro-p-hydroxycinnamate, identified as a potent competitive inhibitor of this enzyme, as well as N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) and benzoate are also presented. These latter crystal structures reveal the location of the active site and suggest a mechanism for the observed YdcE-catalyzed tautomerization reaction. The dimeric arrangement of YdcE represents a new structure in the 4-OT family and demonstrates structural diversity within the 4-OT family not previously reported.
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology*; D007535:Isomerases / Q000037:antagonists & inhibitors / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D011487:Protein Conformation; D016958:Pseudomonas putida / Q000737:chemistry; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein
chemical_list: C021918:4-oxalocrotonate tautomerase; D007535:Isomerases