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首页> 外文期刊>Journal of Molecular Biology >CRYSTAL STRUCTURE OF THE THIAMIN DIPHOSPHATE-DEPENDENT ENZYME PYRUVATE DECARBOXYLASE FROM THE YEAST SACCHAROMYCES CEREVISIAE AT 2.3 ANGSTROM RESOLUTION
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CRYSTAL STRUCTURE OF THE THIAMIN DIPHOSPHATE-DEPENDENT ENZYME PYRUVATE DECARBOXYLASE FROM THE YEAST SACCHAROMYCES CEREVISIAE AT 2.3 ANGSTROM RESOLUTION

机译：酵母糖酵母中硫代磷酸二铵依赖的酶-丙酮酸脱羧酶的晶体结构在2.3 ST分辨率下

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摘要

The crystal structure of pyruvate decarboxylase (EC 4.1.1.1), a thiamin diphosphate-dependent enzyme isolated from Saccharomyces cerevisiae, has been determined and refined to a resolution of 2.3 Angstrom. Pyruvate decarboxylase is a homotetrameric enzyme which crystallizes with two subunits in an asymmetric unit. The structure has been refined by a combination of simulated annealing and restrained least squares to an R factor of 0.165 for 46,787 reflections. As in the corresponding enzyme from Saccharomyces uvarum, the homotetrameric holoenzyme assembly has approximate 222 symmetry In addition to providing more accurate atomic parameters and certainty in the sequence assignments, the high resolution and extensive refinement resulted in the identification of several tightly bound water molecules in key structural positions. These water molecules have low temperature factors and make several hydrogen bonds with protein residues. There are six such water molecules in each cofactor binding site, and one of them is involved in coordination with the required magnesium ion. Another may be involved in the catalytic reaction mechanism. The refined model includes 1074 amino acid residues (two subunits), two thiamin diphosphate cofactors, two magnesium ions associated with cofactor binding and 440 water molecules. From the refined model we conclude that the resting state of the enzyme-cofactor complex is such that the cofactor is already deprotonated at the N4' position of the pyrimidine ring, and is poised to accept a proton from the C2 position of the thiazolium ring. (C) 1996 Academic Press Limited [References: 38]
机译：已确定丙酮酸脱羧酶（EC 4.1.1.1）的晶体结构，该结构是从酿酒酵母中分离的硫胺素二磷酸依赖性酶，并已提纯至2.3埃的分辨率。丙酮酸脱羧酶是同四聚体酶，其在不对称单元中与两个亚基一起结晶。通过模拟退火和约束最小二乘法的组合，对46,787次反射的R因子为0.165，对结构进行了改进。与来自酿酒酵母的相应酶一样，同四聚体全酶装配体具有大约222个对称性。除了在序列分配中提供更准确的原子参数和确定性外，高分辨率和广泛的提纯还导致了关键分子中几个紧密结合的水分子的鉴定结构位置。这些水分子具有低温因子，并与蛋白质残基形成多个氢键。每个辅因子结合位点有六个这样的水分子，其中一个参与与所需镁离子的配位。另一个可能涉及催化反应机理。改进的模型包括1074个氨基酸残基（两个亚基），两个硫胺素二磷酸辅因子，两个与辅因子结合相关的镁离子和440个水分子。从改进的模型中，我们得出结论，酶-辅因子复合物的静止状态使得辅因子在嘧啶环的N4'位处已经去质子化，并准备从噻唑鎓环的C2位接受质子。 （C）1996 Academic Press Limited [参考号：38]

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