New Mechanisms for Regulating Virulence Gene Expression

描述（由申请人提供）：霍乱弧菌引起致命的流行性腹泻病霍乱。其主要毒力因子，毒素共调节菌毛和霍乱毒素的表达，发生通过涉及几个激活蛋白的转录级联反应，并作为细菌毒力的调节范例。ToxT是一种AraC型调节因子，可直接激活主要毒力因子的启动子。toxT的表达需要两对同源的跨膜激活因子ToxRS和TcpPH之间的合作。tcpPH表达的激活通过两种调节蛋白AphA和AphB之间的独特相互作用启动级联反应。AphA是一个新的翼螺旋转录调节因子家族的成员，AphB是一个LysR型激活因子。这些不同启动子的转录激活仅在响应某些环境刺激时发生。这项建议的长期目标是了解这种调节的分子基础，以促进更好的策略来控制霍乱弧菌的感染性。实现这些目标需要了解调控蛋白在其同源启动子中发挥作用以控制基因表达的分子机制，以及最终它们如何受到环境刺激的影响。一个这样的刺激，细胞密度，影响级联通过群体感应调节HapR抑制aphA启动子的表达。目的1阐明HapR抑制aphA表达的机制。有证据表明，这一过程涉及拮抗两种不同的激活剂，Lrp，亮氨酸响应调节蛋白，和VpsR，生物膜调节剂的功能。目的2揭示了新的分子机制，pH值影响的级联的表达，最近发现，AphB在霍乱弧菌的酸耐受性反应中发挥作用，并调节cadC和其他一些基因可能参与这种反应。阐明AphB和酸耐受调节之间的关系将为蛋白质的活性如何受环境刺激的影响提供新的见解。目的3研究霍乱弧菌中AphA和AphB启动毒力基因表达的独特协同机制。这项拟议的工作将促进未来的努力，以确定新的分子，干扰这些监管机构的功能，并可能作为新的抗病毒药。

DESCRIPTION (provided by applicant): Vibrio cholerae causes the fatal epidemic diarrheal disease cholera. The expression of its primary virulence factors, toxin-coregulated pilus and cholera toxin, occurs via a transcriptional cascade involving several activator proteins and serves as a paradigm for the regulation of bacterial virulence. ToxT, an AraC-type regulator, directly activates the promoters of the primary virulence factors. The expression of toxT requires cooperation between two homologous pairs of transmembrane activators, ToxRS and TcpPH. Activation of tcpPH expression initiates the cascade by a unique interaction between two regulatory proteins AphA and AphB. AphA is a member of a new winged-helix transcriptional regulator family and AphB is a LysR-type activator. Transcriptional activation at these various promoter occurs only in response to certain environmental stimuli. The long term goals of this proposal are to understand the molecular basis of this regulation so as to facilitate the development of better strategies to control the infectivity of V. cholerae. Achieving these goals requires an understanding of the molecular mechanisms by which the regulatory proteins function at their cognate promoters to control gene expression and, ultimately, how they are influenced by environmental stimuli. One such stimulus, cell density, influences the cascade through the quorum sensing regulator HapR which represses the expression of the aphA promoter. Aim 1 focuses on elucidating the mechanism by which HapR represses aphA expression. Evidence indicates this process involves antagonizing the function of two distinct activators, Lrp, the leucine responsive regulatory protein, and VpsR, the biofilm regulator. Aim 2 sheds new light on the molecular mechanisms by which pH influences the expression of the cascade by the recent discovery that AphB plays a role in the acid tolerance response in V. cholerae and regulates cadC and a number of other genes potentially involved in this response. Elucidating the relationship between AphB and the regulation of acid tolerance will provide new insights into how the activity of the protein is influenced by environmental stimuli. Aim 3 focuses on investigating the unique cooperative mechanism between AphA and AphB that initiates virulence gene expression in V. cholerae. This proposed work will facilitate future efforts to identify new molecules that interfere with the functions of these regulators and which may serve as novel antivirulence drugs.