title: Crystal structure of the malic enzyme from Ascaris suum complexed with nicotinamide adenine dinucleotide at 2.3 A resolution.
abstract: The structure of the Ascaris suum mitochondrial NAD-malic enzyme in binary complex with NAD has been solved to a resolution of 2.3 A by X-ray crystallography. The structure resembles that of the human mitochondrial enzyme determined in complex with NAD [Xu, Y., Bhargava, G., Wu, H., Loeber, G., and Tong, L. (1999) Structure 7, 877-889]. The enzyme is a tetramer comprised of subunits possessing four domains organized in an "open" structure typical of the NAD-bound form. The subunit organization, as in the human enzyme, is a dimer of dimers. The Ascaris enzyme contains 30 additional residues at its amino terminus relative to the human enzyme. These residues significantly increase the interactions that promote tetramer formation and give rise to different subunit-subunit interactions. Unlike the mammalian enzyme, the Ascaris malic enzyme is not regulated by ATP, and no ATP binding site is observed in this structure. Although the active sites of the two enzymes are similar, residues interacting with NAD differ between the two. The structure is discussed in terms of the mechanism and particularly with respect to previously obtained kinetic and site-directed mutagenesis experiments.
authors.affiliation: Department of Molecular Biology and Immunology, University of North Texas Health Science Center, Fort Worth, Texas 76107, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Coleman
authors.forename: G S Jagannatha
authors.initials: GS
authors.lastname: Rao
authors.forename: E J
authors.initials: EJ
authors.lastname: Goldsmith
authors.forename: Paul F
authors.initials: PF
authors.lastname: Cook
authors.forename: Ben G
authors.initials: BG
authors.lastname: Harris
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001200:Ascaris / Q000201:enzymology*; D001665:Binding Sites; D018360:Crystallography, X-Ray / Q000379:methods; D006801:Humans; D008291:Malate Dehydrogenase / Q000737:chemistry*; D008928:Mitochondria / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data
chemical_list: D000255:Adenosine Triphosphate; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+)