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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Assessment of the allosteric mechanism of aspartate transcarbamoylase based on the crystalline structure of the unregulated catalytic subunit
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Assessment of the allosteric mechanism of aspartate transcarbamoylase based on the crystalline structure of the unregulated catalytic subunit

机译：基于未调节的催化亚基的晶体结构评估天冬氨酸转氨甲酰酶的变构机理

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摘要

The lack of knowledge of the three-dimensional structure of the trimeric, catalytic (C) subunit of aspartate transcarbamoylase (ATCase) has impeded understanding of the allosteric regulation of this enzyme and left unresolved the mechanism by which the active, unregulated C trimers are inactivated on incorporation into the unliganded (taut or T state) holoenzyme. Surprisingly, the isolated C trimer, based on the 1.9 crystal structure reported here,resembles more closcly the trimers in the T state enzymc than in the holoenzyme:bisubstrate-analog complex, which has been considered as the active, relaxed (R) state enzyme. Unlike the C trimer in either the T state or bisubstrate-analogbound holoenzyme, the isolated C trimer lacks 3-fold symmetry, and the active sites are partially disordered. The flexibility of the C trimer, contrasted to the highly constrained T state ATCase, suggests that regulation of the holoenzyme involves modulating the potential for conformational changes essential for catalysis. Large differences in structure between the active C trimer and the holoenzyme:bisubstrate-analog complex call into question the view that this complex represents the activated R state of ATCase.
机译：缺乏对天冬氨酸转氨甲酰酶（ATCase）三聚催化（C）亚基的三维结构的了解，阻碍了对该酶的变构调节的理解，并且尚未解决使活性的，不受调节的C三聚体失活的机制结合到未配体（拉紧或T状态）全酶中。出乎意料的是，基于此处报道的1.9晶体结构的分离的C三聚体比被认为是活性，松弛（R）态酶的全酶：双底物-类似物复合物更类似于T型酶的三聚体。 。与处于T状态或双底物类似物的全酶的C三聚体不同，分离的C三聚体缺乏3倍的对称性，并且活性位点被部分扰乱。与高度受限的T状态ATCase相比，C三聚体的灵活性表明，对全酶的调节涉及调节催化必不可少的构象变化的可能性。活性C三聚体和全酶：双底物-类似物复合物之间在结构上的巨大差异使人质疑该复合物代表ATCase的活化R状态。

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