| - | The crystal structure of pyruvate decarboxylase from Kluyveromyces lactis, has been determined to 2.26 A resolution. Like other yeast enzymes, Kluyveromyces lactis pyruvate decarboxylase is subject to allosteric, substrate activation. Binding of substrate at a regulatory site induces, catalytic activity. This process is accompanied by conformational changes, and subunit rearrangements. In the nonactivated form of the corresponding, enzyme from Saccharomyces cerevisiae, all active sites are solvent, accessible due to the high flexibility of loop regions 106-113 and, 292-301. The binding of the activator pyruvamide arrests these loops., Consequently, two of four active sites become closed. In Kluyveromyces, lactis pyruvate decarboxylase, this half-side closed tetramer is present, even without any activator. However, one of the loops (residues 105-113), which are flexible in nonactivated Saccharomyces cerevisiae pyruvate, decarboxylase, remains flexible. Even though the tetramer assemblies of, both enzyme species are different in the absence of activating agents, their substrate activation kinetics are similar. This implies an, equilibrium between the open and the half-side closed state of yeast, pyruvate decarboxylase tetramers. The completely open enzyme state is, favoured for Saccharomyces cerevisiae pyruvate decarboxylase, whereas the, half-side closed form is predominant for Kluyveromyces lactis pyruvate, decarboxylase. Consequently, the structuring of the flexible loop region, 105-113 seems to be the crucial step during the substrate activation, process of Kluyveromyces lactis pyruvate decarboxylase.
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| - | The crystal structure of pyruvate decarboxylase from Kluyveromyces lactis. Implications for the substrate activation mechanism of this enzyme., Kutter S, Wille G, Relle S, Weiss MS, Hubner G, Konig S, FEBS J. 2006 Sep;273(18):4199-209. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=16939618 16939618]
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