Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, USA.
J Bacteriol. 2024 Jul 25;206(7):e0016824. doi: 10.1128/jb.00168-24. Epub 2024 Jun 13.
Cells use transition metal ions as structural components of biomolecules and cofactors in enzymatic reactions, making transition metal ions integral cellular components. Organisms optimize metal ion concentration to meet cellular needs by regulating the expression of proteins that import and export that metal ion, often in a metal ion concentration-dependent manner. One such regulation mechanism is via riboswitches, which are 5'-untranslated regions of an mRNA that undergo conformational changes to promote or inhibit the expression of the downstream gene, commonly in response to a ligand. The family of bacterial riboswitches shares a conserved aptamer domain that binds manganese ions (Mn). In , the riboswitch precedes and regulates the expression of two different genes: , which based on genetic evidence encodes an Mn exporter, and , which encodes a putative metal ion transporter whose cognate ligand is currently in question. The expression of is upregulated by both elevated concentrations of Mn and alkaline pH. With metal ion measurements and gene expression studies, we demonstrate that the alkalinization of media increases the cytoplasmic manganese pool, which, in turn, enhances expression. The Alx-mediated Mn export prevents the toxic buildup of the cellular manganese, with the export activity maximal at alkaline pH. We pinpoint a set of acidic residues in the predicted transmembrane segments of Alx that play a critical role in Mn export. We propose that Alx-mediated Mn export serves as a primary protective mechanism that fine tunes the cytoplasmic manganese content, especially during alkaline stress.IMPORTANCEBacteria use clever ways to tune gene expression upon encountering certain environmental stresses, such as alkaline pH in parts of the human gut and high concentration of a transition metal ion manganese. One way by which bacteria regulate the expression of their genes is through the 5'-untranslated regions of messenger RNA called riboswitches that bind ligands to turn expression of genes on/off. In this work, we have investigated the roles and regulation of and , the two genes in regulated by the riboswitches, in alkaline pH and high concentration of Mn. This work highlights the intricate ways through which bacteria adapt to their surroundings, utilizing riboregulatory mechanisms to maintain Mn levels amidst varying environmental factors.
细胞将过渡金属离子用作生物分子的结构成分和酶反应的辅助因子,使过渡金属离子成为细胞的基本组成部分。生物体通过调节导入和导出该金属离子的蛋白质的表达来优化金属离子浓度以满足细胞的需求,通常以金属离子浓度依赖的方式进行。一种这样的调节机制是通过核酶开关实现的,核酶开关是 mRNA 的 5'-非翻译区,它通过构象变化来促进或抑制下游基因的表达,通常是对配体做出响应。细菌核酶开关家族共享一个保守的适体结构域,该结构域结合锰离子 (Mn)。在 中, 核酶开关位于并调节两个不同基因的表达: ,根据遗传证据,该基因编码一种 Mn 外排蛋白; ,编码一种假定的金属离子转运蛋白,其同源配体目前尚不清楚。Mn 浓度升高和碱性 pH 均上调 的表达。通过金属离子测量和基因表达研究,我们证明了培养基的碱化增加了细胞质锰库,进而增强了 的表达。Alx 介导的 Mn 外排可防止细胞内锰的毒性积累,其外排活性在碱性 pH 时最大。我们确定了 Alx 预测跨膜片段中的一组酸性残基在 Mn 外排中起着关键作用。我们提出,Alx 介导的 Mn 外排是一种主要的保护机制,可以精细调节细胞质锰含量,尤其是在碱性应激期间。
重要性:细菌在遇到某些环境压力(例如人类肠道某些部位的碱性 pH 和过渡金属离子锰的高浓度)时会巧妙地调节基因表达。细菌调节基因表达的一种方式是通过称为核酶开关的信使 RNA 的 5'-非翻译区,该核酶开关结合配体以开启/关闭基因的表达。在这项工作中,我们研究了 受 核酶开关调节的两个基因 和 的作用和调节,在碱性 pH 和高浓度 Mn 下。这项工作强调了细菌适应周围环境的复杂方式,利用核糖调节机制在不同环境因素中维持 Mn 水平。