title: The β and γ subunits play distinct functional roles in the α2βγ heterotetramer of human NAD-dependent isocitrate dehydrogenase.
abstract: Human NAD-dependent isocitrate dehydrogenase existing as the α2βγ heterotetramer, catalyzes the decarboxylation of isocitrate into α-ketoglutarate in the Krebs cycle, and is allosterically regulated by citrate, ADP and ATP. To explore the functional roles of the regulatory β and γ subunits, we systematically characterized the enzymatic properties of the holoenzyme and the composing αβ and αγ heterodimers in the absence and presence of regulators. The biochemical and mutagenesis data show that αβ and αγ alone have considerable basal activity but the full activity of α2βγ requires the assembly and cooperative function of both heterodimers. α2βγ and αγ can be activated by citrate or/and ADP, whereas αβ cannot. The binding of citrate or/and ADP decreases the S0.5,isocitrateand thus enhances the catalytic efficiencies of the enzymes, and the two activators can act independently or synergistically. Moreover, ATP can activate α2βγ and αγ at low concentration and inhibit the enzymes at high concentration, but has only inhibitory effect on αβ. Furthermore, the allosteric activation of α2βγ is through the γ subunit not the β subunit. These results demonstrate that the γ subunit plays regulatory role to activate the holoenzyme, and the β subunit the structural role to facilitate the assembly of the holoenzyme.
authors.affiliation: National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China.
authors.forename: Tengfei
authors.initials: T
authors.lastname: Ma
authors.affiliation: National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Peng
authors.affiliation: National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Huang
authors.affiliation: School of Life Sciences, Shanghai University, 333 Nanchen Road, Shanghai 200444, China.
authors.forename: Yabing
authors.initials: Y
authors.lastname: Liu
authors.affiliation: National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China.|School of Life Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210, China.|Shanghai Science Research Center, Chinese Academy of Sciences, 333 Haike Road, Shanghai 201210, China.|Collaborative Innovation Center for Genetics and Development, Fudan University, 2005 Songhu Road, Shanghai 200438, China.
authors.forename: Jianping
authors.initials: J
authors.lastname: Ding
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000495:Allosteric Site; D019343:Citric Acid / Q000378:metabolism; D006801:Humans; D007521:Isocitrate Dehydrogenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism
chemical_list: D021122:Protein Subunits; D019343:Citric Acid; D000244:Adenosine Diphosphate; D007521:Isocitrate Dehydrogenase