Câmara Amanda Souza, Horjales Eduardo
Departamento de Física e ciência interdisciplinar, Instituto de Física de São Carlos; Universidade de São Paulo, São Carlos, SP, Brasil.
PLoS One. 2018 Feb 22;13(2):e0192826. doi: 10.1371/journal.pone.0192826. eCollection 2018.
M. tuberculosis oxidation sense Regulator (MosR) is a transcriptional regulator from Mycobacterium tuberculosis. It senses the environment oxidation and regulates the expression of a secreted oxidoreductase, thus defending the bacilli against oxidative stress from the phagosome. While most of the members of the Multiple antibiotics resistance Regulator (MarR) family are ligand-responsive, MosR may dissociate from its DNA site upon formation of an intrachain disulphide bond. However, the structure of MosR in its oxidized state is not known, and it is not clear how the formation of this disulphide bond would lead to the conformational changes required for dissociation of the DNA. Nonetheless, MosR presents two crystallographically resolved conformations in its reduced state: bound and unbound to DNA. We managed to simulate MosR unbound to the DNA, both in the presence and in the absence of the disulphide bond. Our results indicate that this disulphide bond precludes the N-terminal residues from adopting a conformation that stands in-between the helix α1 and the DNA binding domain (DBD) from the other chain. Once this conformation is achieved in the reduced state, this DBD detaches from the dimerization domain and becomes more flexible, being able to perform motions with higher amplitude and higher degree of collectivity. Only then, MosR may achieve a conformation where its recognition helices fit into the major grooves of its DNA site. The analysis of the collective motions performed by MosR, during the different situations sampled by the molecular dynamics (MDs), was only possible by the method of filtering harmonic modes with specific frequencies. The frequency of the collective motions performed by the DBD of MosR in the reduced state to achieve a DNA-binding conformation is in the range of 20 to 50 MHz, but it may be associated to more sporadic events since it requires the combination of a suitable conformation of the N-terminal residues.
结核分枝杆菌氧化感应调节因子（MosR）是来自结核分枝杆菌的一种转录调节因子。它感知环境氧化并调节一种分泌型氧化还原酶的表达，从而保护杆菌免受来自吞噬体的氧化应激。虽然多重抗生素耐药调节因子（MarR）家族的大多数成员是配体响应型的，但MosR可能在形成链内二硫键后从其DNA位点解离。然而，MosR氧化态的结构尚不清楚，并且不清楚这种二硫键的形成如何导致DNA解离所需的构象变化。尽管如此，MosR在其还原态呈现出两种晶体学解析的构象：与DNA结合和未与DNA结合。我们成功模拟了未与DNA结合的MosR，包括存在和不存在二硫键的情况。我们的结果表明，这种二硫键阻止了N端残基采取一种介于α1螺旋和来自另一条链的DNA结合结构域（DBD）之间的构象。一旦在还原态达到这种构象，这个DBD就会从二聚化结构域分离并变得更加灵活，能够进行幅度更大、集体性更高的运动。只有到那时，MosR才可能达到一种构象，使其识别螺旋适合其DNA位点的大沟。通过用特定频率过滤谐波模式的方法，才能够分析在分子动力学（MDs）采样的不同情况下MosR进行的集体运动。MosR还原态的DBD为实现DNA结合构象而进行的集体运动频率在20至50兆赫兹范围内，但它可能与更零星的事件相关，因为它需要N端残基的合适构象的组合。
