Department of Oral Biology, University of Florida, Gainesville, FL, 32610, USA.
Mol Microbiol. 2018 Aug;109(3):345-364. doi: 10.1111/mmi.13989. Epub 2018 Jul 31.
Streptococcus mutans displays complex regulation of natural genetic competence. Competence development in S. mutans is controlled by a peptide derived from ComS (XIP); which along with the cytosolic regulator ComR controls the expression of the alternative sigma factor comX, the master regulator of competence development. Recently, a gene embedded within the coding region of comX was discovered and designated xrpA (comX regulatory peptide A). XrpA was found to be an antagonist of ComX, but the mechanism was not established. In this study, we reveal through both genomic and proteomic techniques that XrpA is the first described negative regulator of ComRS systems in streptococci. Transcriptomic and promoter activity assays in the ΔxrpA strain revealed an up-regulation of genes controlled by both the ComR- and ComX-regulons. An in vivo protein crosslinking and in vitro fluorescent polarization assays confirmed that the N-terminal region of XrpA were found to be sufficient in inhibiting ComR-XIP complex binding to ECom-box located within the comX promoter. This inhibitory activity was sufficient for decreases in PcomX activity, transformability and ComX accumulation. XrpA serving as a modulator of ComRS activity ultimately results in changes to subpopulation behaviors and cell fate during competence activation.
变形链球菌表现出复杂的天然遗传感受态的调控。变形链球菌的感受态发育受来自 ComS（XIP）的肽控制；该肽与细胞质调节剂 ComR 一起控制替代 sigma 因子 comX 的表达，该因子是感受态发育的主要调节剂。最近，在 comX 的编码区内发现了一个基因，并将其命名为 xrpA（comX 调节肽 A）。发现 XrpA 是 ComX 的拮抗剂，但机制尚未确定。在这项研究中，我们通过基因组和蛋白质组学技术揭示了 XrpA 是链球菌中第一个描述的 ComRS 系统的负调节剂。在 ΔxrpA 菌株中的转录组和启动子活性测定显示，ComR 和 ComX 调节子控制的基因上调。体内蛋白交联和体外荧光偏振测定证实，XrpA 的 N 端区域足以抑制 ComR-XIP 复合物与位于 comX 启动子内的 ECom 盒结合。这种抑制活性足以降低 PcomX 活性、转化能力和 ComX 积累。XrpA 作为 ComRS 活性的调节剂，最终导致感受态激活过程中亚群行为和细胞命运的改变。
