Choi Garam, Kim Dukyun, Im Hanhyeok, Choi Sang Ho
National Research Laboratory of Molecular Microbiology and Toxicology, Department of Agricultural Biotechnology, Seoul National University, Seoul, South Korea.
Center for Food and Bioconvergence, Seoul National University, Seoul, South Korea.
Front Microbiol. 2021 May 21;12:681196. doi: 10.3389/fmicb.2021.681196. eCollection 2021.
Nitric oxide (NO) is an important antimicrobial effector produced by the host innate immune system to counteract invading pathogens. To survive and establish a successful infection, a fulminating human pathogen expresses the gene encoding an NO dioxygenase in an NO-responsive manner. In this study, we identified an Rrf2-family transcriptional regulator NsrR that is predicted to contain the Fe-S cluster coordinated by three cysteine residues. Transcriptome analysis showed that NsrR controls the expression of multiple genes potentially involved in nitrosative stress responses. Particularly, NsrR acts as a strong repressor of transcription and relieves the repression of upon exposure to NO. Notably, and are transcribed divergently, and their promoter regions overlap with each other. Molecular biological analyses revealed that NsrR directly binds to this overlapping promoter region, which is alleviated by loss of the Fe-S cluster, leading to the subsequent derepression of under nitrosative stress. We further found that a leucine-responsive regulatory protein (Lrp) negatively regulates in an NsrR-dependent manner by directly binding to the promoter region, presumably resulting in a DNA conformation change to support the repression by NsrR. Meanwhile, a cyclic AMP receptor protein (CRP) positively regulates probably through repression of and by directly binding to each promoter region in a sequential cascade. Altogether, this collaborative regulation of NsrR along with Lrp and CRP enables an elaborate control of transcription, contributing to survival under host-derived nitrosative stress and thereby the pathogenesis of .
一氧化氮（NO）是宿主先天免疫系统产生的一种重要抗菌效应分子，用于对抗入侵的病原体。为了生存并成功建立感染，一种烈性人类病原体以NO响应的方式表达编码NO双加氧酶的基因。在本研究中，我们鉴定了一种Rrf2家族转录调节因子NsrR，预计其含有由三个半胱氨酸残基配位的铁硫簇。转录组分析表明，NsrR控制多个可能参与亚硝化应激反应的基因的表达。特别地，NsrR作为转录的强抑制因子，并在暴露于NO时解除对其的抑制。值得注意的是，和以发散方式转录，并且它们的启动子区域相互重叠。分子生物学分析表明，NsrR直接结合到这个重叠的启动子区域，铁硫簇的缺失可缓解这种结合，从而导致在亚硝化应激下随后的去抑制。我们进一步发现，亮氨酸响应调节蛋白（Lrp）通过直接结合启动子区域以NsrR依赖的方式负调节，推测这会导致DNA构象改变以支持NsrR的抑制作用。同时，环磷酸腺苷受体蛋白（CRP）可能通过依次级联直接结合每个启动子区域抑制和来正向调节。总之，NsrR与Lrp和CRP的这种协同调节能够精细控制转录，有助于在宿主来源的亚硝化应激下生存，从而促进的发病机制。
