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首页> 外文学位 >Allosteric and conformational transitions in the tryptophan synthase bienzyme complex, and the role of monovalent cation activation by probing the cation free state of the enzyme.
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Allosteric and conformational transitions in the tryptophan synthase bienzyme complex, and the role of monovalent cation activation by probing the cation free state of the enzyme.

机译：色氨酸合酶双酶复合物中的变构和构象转变，以及通过探测酶的阳离子游离态来激活单价阳离子的作用。

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摘要

The tryptophan synthase alpha2beta2 bienzyme complex is a wonderful model to study, allosteric regulation of catalysis, substrate channeling, and structure-function relationships. This system requires the presence of a Monovalent cation (MVC) for activation, and undergoes a conformational transition from and open conformation, to a closed conformation. Both the alpha- and beta-subunits undergo a conformational transition, and it has been shown that a transition of one subunit assists in lowering the energy of the transition of the other subunit. Furthermore, these conformational transitions are triggered by the formation of covalent chemical intermediates in the pathway of L-Trp synthesis. The cleavage of 3-indole-D-glycerol 3'-phosphate (IGP) to D-glyceraldehyde 3-phosphate (G3P) and indole (alpha-reaction) occurs only when both the alpha- and beta-subunits are in a closed conformation. The beta-subunit undergoes a conformational transition upon the elimination of the hydroxyl of L-Ser, forming the E(A-A) species, the species which reacts with indole generated in the alpha-reaction. This allosteric communication requires the binding of a MVC for proper function, and it is the objective of this dissertation to describe how the MVC binding alters this communication, and how cation size plays a role. The studies presented herein establish the following; (a) the binding of Cs+ appears to be stabilize the closed conformation of the beta-subunit while Na + appears to preferentially stabilize the open conformation, (b) the MVC-Free from of the enzyme is impaired mainly by displaying a decreased affinity towards beta-site nucleophiles, and greatly inhibiting stage II of the beta-reaction, (c) the reaction of L-Ser with the MVC-Free E(Ain), the is the existence of an inactive E(A-A) which is formed after the initial formation of the active branch of this species. This dissertation examines the structural effects exerted on the beta-active site via the MVC site, and sheds much light on the mechanism of MVC induced activation.
机译：色氨酸合酶α2β2双酶复合物是研究，催化的变构调节，底物通道和结构功能关系的绝佳模型。该系统需要存在用于激活的单价阳离子（MVC），并经历从开放构象到封闭构象的构象转变。 α-和β-亚基都经历构象转变，并且已经显示一个亚基的转变有助于降低另一亚基的转变能量。此外，这些构象转变是由L-Trp合成途径中共价化学中间体的形成触发的。 3-吲哚-D-甘油3'-磷酸（IGP）裂解为D-甘油醛3-磷酸（G3P）和吲哚（α-反应）的裂解仅在α和β亚基均处于闭合构象时发生。 β-亚基在消除L-Ser的羟基后经历构象转变，形成E（A-A）物种，该物种与在α反应中生成的吲哚发生反应。这种变构通讯需要MVC的结合才能发挥适当的功能，因此，本论文的目的是描述MVC的结合如何改变这种通讯以及阳离子的大小如何发挥作用。本文介绍的研究建立了以下内容； （a）Cs +的结合似乎稳定了β-亚基的封闭构象，而Na +似乎优先稳定了开放构象，（b）缺乏MVC的酶主要是由于对Cs +的亲和力降低而受到损害β-位亲核试剂，并大大抑制β-反应的第二阶段，（c）L-Ser与不含MVC的E（Ain）的反应，是在形成无活性E（AA）之后该物种活跃分支的最初形成。本文研究了通过MVC位点作用于β-活性位点的结构效应，并为MVC诱导的激活机制提供了很多启示。

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  • 作者

    Dierkers, Adam Timothy.;

  • 作者单位

    University of California, Riverside.;

  • 授予单位 University of California, Riverside.;
  • 学科 Chemistry Biochemistry.
  • 学位 Ph.D.
  • 年度 2008
  • 页码 142 p.
  • 总页数 142
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 生物化学;
  • 关键词

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