Zinc dependent conformational changes in AdcR and their impact on DNA binding

肺炎链球菌是一种革兰氏阳性兼性厌氧菌，定植于上呼吸道。 大多数人类的活动区域。像肺炎链球菌这样的病原体依靠它们的宿主为生长提供所有的营养，这 包括几个过渡金属离子。锌(II)离子是所有生命系统所需的微量营养素。细胞内 肺炎链球菌体内的锌离子浓度受两个转录因子(TF)调控。这些蛋白质被称为AdcR和 SczA以高亲和力结合锌离子。在这两种蛋白质中，锌(II)结合事件诱导了结构上的 使这些锌转铁蛋白与其特定DNA启动子的亲和力显著增加的蛋白质的变化 地区。正是这一过程调节了肺炎链球菌体内一系列负责锌离子稳态的蛋白质。 锌离子、转铁蛋白和DNA之间的化学平衡是治疗药物开发的有吸引力的目标，其中 影响肺炎链球菌适应宿主内新位置的能力可以直接影响其毒力。 AdcR在其金属结合区与两个锌离子结合，该结合部位通过一系列 蛋白质中非结构环之间的分子内相互作用。具体地说，站点1是协调的 饱和四面体位置，所有四个位置都通过氨基酸侧链残基配位。站点2还 采用四面体配位方式，但其中一个位置被水分子占据，这提供了 一个扰乱这个系统的机会。与这一提议相关的中心假设是锌(II)结合 在AdcR(Lys22到Ser38)中诱导动态环的组织，从而将蛋白质锁定到有利的DNA中 结合构象。突变(目标1)或化学试剂(目标2)对该环结构的扰动可以 显著影响了Zn2AdcR的结构，导致了Zn2AdcR/DNA结合热力学的变化。

Streptococcus pneumoniae is a Gram-positive, facultative anaerobic bacteria that colonizes in the upper respiratory tract of most humans. Pathogens like S. pneumoniae rely on their host to provide all nutrients for growth, which includes several transition metal ions. Zinc(II) ions are required micronutrients for all living systems. The intracellular Zn2+ concentration in S. pneumoniae is regulated by two transcription factors (TFs). These proteins, termed AdcR and SczA, are known to bind Zn2+ ions with high affinity. In both proteins, the zinc(II) binding events induce a structural change in the protein that affords a dramatic increase in the affinity of these Zn-TFs for their specific DNA promotor regions. It is this process that regulates a series of proteins responsible for Zn2+ homeostasis within S. pneumoniae. The chemical equilibria between Zn2+, TFs, and DNA are attractive targets for therapeutic agent development, where impacting S. pneumoniae’s ability to adapt to new locations within a host can directly impact its virulence. AdcR binds two Zn2+ ions in its metal binding domain, and this binding site is stabilized through a series of intramolecular interactions between an unstructured loop in the protein. Specifically, site 1 is a coordinatively saturated tetrahedral site, where all four positions are coordinated through amino-acid side chain residues. Site 2 also adopts a tetrahedral coordination mode, however one of these sites is occupied by a water molecule, which provides an opportunity to disrupt this system. The central hypothesis associated with this proposal is that zinc(II) binding induces an organization of a dynamic loop in AdcR (Lys22 to Ser38), which locks the protein into a favorable DNA binding conformation. Perturbations to the structure of this loop by mutation (aim 1) or chemical agents (aim 2) can impact the Zn2AdcR structure significantly leading to changes in the thermodynamics of Zn2AdcR/DNA binding.