Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Infect Immun. 2010 Mar;78(3):1109-22. doi: 10.1128/IAI.00363-09. Epub 2009 Dec 14.
Outer membrane iron receptors are some of the major surface entities that are critical for meningococcal pathogenesis. The gene encoding the meningococcal hemoglobin receptor, HmbR, is both independently transcribed and transcriptionally linked to the upstream gene hemO, which encodes a heme oxygenase. The MisR/S two-component system was previously determined to regulate hmbR transcription, and its hemO and hmbR regulatory mechanisms were characterized further here. The expression of hemO and hmbR was downregulated in misR/S mutants under both iron-replete and iron-restricted conditions, and the downregulation could be reversed by complementation. No significant changes in expression of other iron receptors were detected, suggesting that the MisR/S system specifically regulates hmbR. When hemoglobin was the sole iron source, growth defects were detected in the mutants. Primer extension analysis identified a promoter upstream of the hemO-associated Correia element (CE) and another promoter at the proximal end of CE, and processed transcripts previously identified for other cotranscribed CEs were also detected, suggesting that there may be posttranscriptional regulation. MisR directly interacts with sequences upstream of the CE and upstream of the hmbR Fur binding site and thus independently regulates hemO and hmbR. Analysis of transcriptional reporters of hemO and hmbR further demonstrated the positive role of the MisR/S system and showed that the transcription of hmbR initiated from hemO was significantly reduced. A comparison of the effects of the misS mutation under iron-replete and iron-depleted conditions suggested that activation by the MisR/S system and iron-mediated repression by Fur act independently. Thus, the expression of hemO and hmbR is coordinately controlled by multiple independent regulatory mechanisms, including the MisR/S two-component system.
外膜铁受体是脑膜炎奈瑟菌发病机制的重要表面实体之一。编码脑膜炎奈瑟菌血红蛋白受体 HmbR 的基因既独立转录，又与编码血红素加氧酶的上游基因 hemO 转录连锁。先前已经确定 MisR/S 双组分系统调节 hmbR 转录，并且进一步研究了其 hemO 和 hmbR 的调控机制。在铁充足和铁限制条件下，misR/S 突变体中的 hemO 和 hmbR 表达均下调，互补可逆转这种下调。未检测到其他铁受体表达的显著变化，表明 MisR/S 系统特异性调节 hmbR。当血红蛋白是唯一的铁源时，突变体中检测到生长缺陷。引物延伸分析鉴定了 hemO 相关 Correia 元件 (CE) 上游的启动子和 CE 近端的另一个启动子，并且还检测到先前鉴定的其他共转录 CE 的加工转录本，表明可能存在转录后调控。MisR 直接与 CE 上游和 hmbR Fur 结合位点上游的序列相互作用，因此独立调节 hemO 和 hmbR。hemO 和 hmbR 的转录报告分析进一步证明了 MisR/S 系统的积极作用，并且表明 hmbR 的转录从 hemO 显著减少。在铁充足和缺铁条件下比较 misS 突变的影响表明，MisR/S 系统的激活和 Fur 介导的铁抑制独立作用。因此，hemO 和 hmbR 的表达受到多个独立调控机制的协调控制，包括 MisR/S 双组分系统。
