On the role of αThr183 in the allosteric regulation and catalytic mechanism of tryptophan synthase
On the role of αThr183 in the allosteric regulation and catalytic mechanism of tryptophan synthase
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DOI：
10.1016/s0022-2836(02)01109-9
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发表时间：
2002-12-06
影响因子：
5.6
通讯作者：
Schlichting, I
中科院分区：
文献类型：
--
作者：
Kulik, V;Weyand, M;Schlichting, I
吡哆醛5 '-磷酸依赖性色氨酸合酶α（2）β（2）复合物的催化活性和底物通道作用受变构相互作用调节，该变构相互作用调节酶在催化循环期间在开放、低活性和封闭、高活性状态之间的转换。高度保守的alphaThr 183残基是环alphaL 6的一部分，位于α-活性位点旁边，并形成α-β亚基界面的一部分。通过对alphaThr 183 Val的动力学和晶体结构的分析，研究了alphaThr 183在α位催化和I变构调节中的相互作用.突变体显示出强烈受损的变构α-β通讯，α反应的催化活性降低了100倍，而β活性不受影响。结构工作确定缺失亚基间信号传导的基础是即使在α-亚基配体、3-吲哚基-D-甘油3 '-磷酸或3-吲哚基丙醇3'-磷酸存在下也缺乏环α L 6闭合。α-活性降低的结构基础源于aThr 183和催化残基alphaAsp 60之间的氢键缺失。(C)2002爱思唯尔科技有限公司版权所有。
The catalytic activity and substrate channeling of the pyridoxal 5'-phosphate-dependent tryptophan synthase alpha(2)beta(2) complex is regulated by allosteric interactions that modulate the switching of the enzyme between open, low activity and closed, high activity states during the catalytic cycle. The highly conserved alphaThr183 residue is part of loop alphaL6 and is located next to the alpha-active site and forms part of the alpha-beta subunit interface. The role of the interactions of alphaThr183 in alpha-site catalysis and I allosteric regulation was investigated by analyzing the kinetics and crystal structures of the isosteric mutant alphaThr183Val. The mutant displays strongly impaired allosteric alpha-beta communication, and the catalytic activity of the alpha-reaction is reduced one hundred fold, whereas the beta-activity is not affected. The structural work establishes that the basis for the missing inter-subunit signaling is the lack of loop alphaL6 closure even in the presence of the alpha-subunit ligands, 3-indolyl-D-glycerol 3'-phosphate, or 3-indolylpropanol 3'-phosphate. The structural basis for the reduced alpha-activity has its origins in the missing hydrogen bond between aThr183 and the catalytic residue, alphaAsp60. (C) 2002 Elsevier Science Ltd. All rights reserved.