title: Structural studies of the pigeon cytosolic NADP(+)-dependent malic enzyme.
abstract: Malic enzymes are widely distributed in nature, and have important biological functions. They catalyze the oxidative decarboxylation of malate to produce pyruvate and CO(2) in the presence of divalent cations (Mg(2+), Mn(2+)). Most malic enzymes have a clear selectivity for the dinucleotide cofactor, being able to use either NAD(+) or NADP(+), but not both. Structural studies of the human mitochondrial NAD(+)-dependent malic enzyme established that malic enzymes belong to a new class of oxidative decarboxylases. Here we report the crystal structure of the pigeon cytosolic NADP(+)-dependent malic enzyme, in a closed form, in a quaternary complex with NADP(+), Mn(2+), and oxalate. This represents the first structural information on an NADP(+)-dependent malic enzyme. Despite the sequence conservation, there are large differences in several regions of the pigeon enzyme structure compared to the human enzyme. One region of such differences is at the binding site for the 2'-phosphate group of the NADP(+) cofactor, which helps define the cofactor selectivity of the enzymes. Specifically, the structural information suggests Lys362 may have an important role in the NADP(+) selectivity of the pigeon enzyme, confirming our earlier kinetic observations on the K362A mutant. Our structural studies also revealed differences in the organization of the tetramer between the pigeon and the human enzymes, although the pigeon enzyme still obeys 222 symmetry.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
authors.forename: Zhiru
authors.initials: Z
authors.lastname: Yang
authors.forename: Hailong
authors.initials: H
authors.lastname: Zhang
authors.forename: Hui-Chi
authors.initials: HC
authors.lastname: Hung
authors.forename: Chen-Chin
authors.initials: CC
authors.lastname: Kuo
authors.forename: Li-Chu
authors.initials: LC
authors.lastname: Tsai
authors.forename: Hanna S
authors.initials: HS
authors.lastname: Yuan
authors.forename: Wei-Yuan
authors.initials: WY
authors.lastname: Chou
authors.forename: Gu-Gang
authors.initials: GG
authors.lastname: Chang
authors.forename: Liang
authors.initials: L
authors.lastname: Tong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D010856:Columbidae; D003460:Crystallization; D018360:Crystallography, X-Ray; D003600:Cytosol / Q000201:enzymology*; D006801:Humans; D008099:Liver / Q000201:enzymology*; D008291:Malate Dehydrogenase / Q000737:chemistry* / Q000302:isolation & purification; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009249:NADP / Q000737:chemistry; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D009249:NADP; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+)