title: Dual functional roles of ATP in the human mitochondrial malic enzyme.
abstract: Human mitochondrial malic enzyme is a regulatory enzyme with ATP as an inhibitor. Structural studies reveal that the enzyme has two ATP-binding sites, one at the NAD(+)-binding site in the active center and the other at the exo site in the tetramer interface. Inhibition of the enzyme activity is due to the competition between ATP and NAD(+) for the nucleotide-binding site at the active center with an inhibition constant of 81 microM. Binding of the ATP molecule at the exo site, on the other hand, is important for the maintenance of the quaternary structural integrity. The enzyme exists in solution at neutral pH and at equilibrium of the dimer and tetramer with a dissociation constant (K(TD)) of 0.67 microM. ATP, at a physiological concentration, shifts the equilibrium toward tetramer and decreases the K(TD) by many orders of magnitude. Mutation of a single residue Arg542 at the tetrameric interfacial exo site resulted in dimeric mutants. ATP thus has dual functional roles in the mitochondrial malic enzyme.
authors.affiliation: Faculty of Life Sciences, Institute of Biochemistry, Structure Biology Program, and Proteome Research Center, National Yang-Ming University, Taipei 112, Taiwan.
authors.forename: Wen-Chi
authors.initials: WC
authors.lastname: Hsu
authors.forename: Hui-Chih
authors.initials: HC
authors.lastname: Hung
authors.forename: Liang
authors.initials: L
authors.lastname: Tong
authors.forename: Gu-Gang
authors.initials: GG
authors.lastname: Chang
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D001665:Binding Sites; D019281:Dimerization; D006801:Humans; D007700:Kinetics; D008291:Malate Dehydrogenase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D009243:NAD / Q000378:metabolism; D020836:Protein Structure, Quaternary / Q000187:drug effects
chemical_list: D008293:Malates; D024101:Mitochondrial Proteins; D009243:NAD; C030298:malic acid; D000255:Adenosine Triphosphate; D008291:Malate Dehydrogenase; C034544:D-malate dehydrogenase (decarboxylating)