Aubee Joseph I, Nurse Jalisa, Lewis Dale, Tai Chin-Hsien, Thompson Karl M
Department of Microbiology, College of Medicine, Howard University, Washington, DC 20059, USA.
Department of Biology, Howard University, Washington, DC 20059, USA.
Int J Mol Sci. 2025 Jun 30;26(13):6318. doi: 10.3390/ijms26136318.
The envelope stress response in is primarily governed by the sigma factor RpoE (σ), which activates protective genes upon membrane perturbation. Under non-stress conditions, σ is sequestered by its anti-sigma factor RseA. In this study, we identify an unexpected role for the nitric-oxide-sensing repressor NsrR in dampening σ activity and repressing σ-dependent small RNAs, including , , and . Overexpression of represses transcription from σ-dependent promoters and phenocopies σ inactivation, resulting in filamentous morphology and growth defects. Conversely, Δ de-represses σ targets, with additive effects in mutants-supporting an RseA-independent regulatory role. Time-course analysis shows NsrR represses σ activity, with kinetics comparable to those of RseA. While in vitro assays failed to detect robust NsrR binding to σ target promoters, NsrR directly interacts with σ in bacterial two-hybrid assays. Structural modeling using AlphaFold3 supports a plausible NsrR-RpoE interaction interface. These findings suggest that NsrR functions as a noncanonical anti-sigma-like modulator of σ, integrating redox and envelope stress signals to maintain membrane homeostasis.
中的包膜应激反应主要由σ因子RpoE（σ）调控，它在膜受到扰动时激活保护性基因。在非应激条件下，σ被其抗σ因子RseA隔离。在本研究中，我们发现一氧化氮感应阻遏物NsrR在抑制σ活性和抑制σ依赖性小RNA（包括、和）方面具有意想不到的作用。的过表达抑制了来自σ依赖性启动子的转录，并模拟了σ失活，导致丝状形态和生长缺陷。相反，Δ去抑制σ靶标，在突变体中具有累加效应，支持了一种不依赖RseA的调控作用。时间进程分析表明NsrR抑制σ活性，其动力学与RseA相当。虽然体外实验未能检测到NsrR与σ靶标启动子的强结合，但在细菌双杂交实验中NsrR直接与σ相互作用。使用AlphaFold3进行的结构建模支持了一个合理的NsrR-RpoE相互作用界面。这些发现表明，NsrR作为σ的非典型抗σ样调节剂发挥作用，整合氧化还原和包膜应激信号以维持膜稳态。
