Dias Marcio V B, Borges Júlio C, Ely Fernanda, Pereira José H, Canduri Fernanda, Ramos Carlos H I, Frazzon Jeverson, Palma Mário S, Basso Luis A, Santos Diógenes S, de Azevedo Walter F
Programa de Pós-Graduação em Biofísica Molecular, Departamento de Física, UNESP, São José do Rio Preto, SP 15054-000, Brazil.
J Struct Biol. 2006 May;154(2):130-43. doi: 10.1016/j.jsb.2005.12.008. Epub 2006 Jan 17.
In bacteria, fungi, plants, and apicomplexan parasites, the aromatics compounds, such as aromatics amino acids, are synthesized through seven enzymes from the shikimate pathway, which are absent in mammals. The absence of this pathway in mammals make them potential targets for development of new therapy against infectious diseases, such as tuberculosis, which is the world's second commonest cause of death from infectious disease. The last enzyme of shikimate pathway is the chorismate synthase (CS), which is responsible for conversion of the 5-enolpyruvylshikimate-3-phosphate to chorismate. Here, we report the crystallographic structure of CS from Mycobacterium tuberculosis (MtCS) at 2.65 A resolution. The MtCS structure is similar to other CS structures, presenting beta-alpha-beta sandwich structural topology, in which each monomer of MtCS consists of a central helical core. The MtCS can be described as a tetramer formed by a dimer of dimers. However, analytical ultracentrifugation studies suggest the MtCS is a dimer with a more asymmetric shape than observed on the crystallographic dimer and the existence of a low equilibrium between dimer and tetramer. Our results suggest that the MtCS oligomerization is concentration dependent and some conformational changes must be involved on that event.
在细菌、真菌、植物和顶复门寄生虫中，芳香族化合物，如芳香族氨基酸，是通过莽草酸途径中的七种酶合成的，而哺乳动物体内不存在这些酶。哺乳动物体内缺乏该途径使其成为开发针对传染病（如结核病，结核病是全球第二大常见传染病致死病因）新疗法的潜在靶点。莽草酸途径的最后一种酶是分支酸合酶（CS），它负责将5-烯醇丙酮酸莽草酸-3-磷酸转化为分支酸。在此，我们报告了结核分枝杆菌CS（MtCS）在2.65 Å分辨率下的晶体结构。MtCS的结构与其他CS结构相似，呈现β-α-β夹心结构拓扑，其中MtCS的每个单体由一个中央螺旋核心组成。MtCS可描述为由二聚体的二聚体形成的四聚体。然而，分析超速离心研究表明，MtCS是一种二聚体，其形状比晶体学二聚体中观察到的更不对称，并且在二聚体和四聚体之间存在低平衡。我们的结果表明，MtCS的寡聚化依赖于浓度，并且该过程必定涉及一些构象变化。
