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標題: Structural characteristics of the nonallosteric human cytosolic malic enzyme
作者: Hsieh, Ju-Yi
Li, Shao-Yu
Chen, Meng-Chun
Yang, Pai-Chun
Chen, Hui-Yi
Chan, Nei-Li
Liu, Jyung-Hurng
Hung, Hui-Chih
關鍵字: Allosteric activation;Fumarate-binding site;Kinetics;Malic enzyme;Mutagenesis;Quaternary structural stability
Project: Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, Volume 1844, Issue 10, Page(s) 1773-1783.
Human cytosolic NADP(+)-dependent malic enzyme (c-NADP-ME) is neither a cooperative nor an allosteric enzyme, whereas mitochondrial NAD(P)(+)-dependent malic enzyme (m-NAD(P)-ME) is allosterically activated by fumarate. This study examines the molecular basis for the different allosteric properties and quaternary structural stability of m-NAD(P)-ME and c-NADP-ME. Multiple residues corresponding to the fumarate-binding site were mutated in human c-NADP-ME to correspond to those found in human m-NAD(P)-ME. Additionally, the crystal structure of the apo (ligand-free) human c-NADP-ME conformation was determined. Kinetic studies indicated no significant difference between the wild-type and mutant enzymes in Km,NADP, Km,malate, and kcat. A chimeric enzyme, [51-105]_c-NADP-ME, was designed to include the putative fumarate-binding site of m-NAD(P)-ME at the dimer interface of c-NADP-ME; however, this chimera remained nonallosteric. In addition to fumarate activation, the quaternary structural stability of c-NADP-ME and m-NAD(P)-ME is quite different; c-NADP-ME is a stable tetramer, whereas m-NAD(P)-ME exists in equilibrium between a dimer and a tetramer. The quaternary structures for the S57K/N59E/E73K/S102D and S57K/N59E/E73K/S102D/H74K/D78P/D80E/D87G mutants of c-NADP-ME are tetrameric, whereas the K57S/E59N/K73E/D102S m-NAD(P)-ME quadruple mutant is primarily monomeric with some dimer formation. These results strongly suggest that the structural features near the fumarate-binding site and the dimer interface are highly related to the quaternary structural stability of c-NADP-ME and m-NAD(P)-ME. In this study, we attempt to delineate the structural features governing the fumarate-induced allosteric activation of malic enzyme.
ISSN: 15709639
DOI: 10.1016/j.bbapap.2014.06.019
Appears in Collections:基因體暨生物資訊學研究所

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