Molle Virginie, Saint Nathalie, Campagna Sylvie, Kremer Laurent, Lea Edward, Draper Philip, Molle Gérard
IBCP, UMR 5086 CNRS, University of Lyon, 69367 Lyon, France.
Mol Microbiol. 2006 Aug;61(3):826-37. doi: 10.1111/j.1365-2958.2006.05277.x.
Mycobacteria are characterized by an unusual cell wall that controls nutrient and small hydrophilic compound permeability. Porin-like proteins are necessary to ensure the transport of molecules into the cell. Here, we investigated the pore-forming properties of OmpATb, a porin from Mycobacterium tuberculosis, in lipid bilayers. Multi-channel experiments showed an asymmetric behaviour with channel closures at negative critical voltages (Vc) and a strong decrease in Vc at acidic pH. Single-channel experiments gave conductance values of about 850 +/- 80 pS in 1 M KCl and displayed a weak cationic selectivity in 4-8 pH range. The production and characterization of a series of truncated OmpATb proteins, showed that the central domain (OmpATb73-220) was sufficient to induce the ion channel properties of the native protein in lipid bilayers, i.e. asymmetric insertion, pH-dependent voltage closure, cationic selectivity and similar conductance values in 1 M KCl. Western blot analysis suggests that the presence of OmpATb is only restricted to certain pathogenic species. Therefore, the propensity of channels of native OmpATb to close at low pH may represent an intrinsic property allowing pathogenic mycobacteria to adapt and survive to mildly acidic conditions, such as those encountered within the macrophage phagosome.
分枝杆菌的特征在于其独特的细胞壁，该细胞壁控制营养物质和小的亲水性化合物的通透性。孔蛋白样蛋白对于确保分子进入细胞的运输是必要的。在此，我们研究了结核分枝杆菌孔蛋白OmpATb在脂质双层中的成孔特性。多通道实验显示出一种不对称行为，即在负临界电压（Vc）下通道关闭，并且在酸性pH下Vc显著降低。单通道实验在1 M KCl中给出的电导值约为850 +/- 80 pS，并且在4 - 8的pH范围内表现出较弱的阳离子选择性。一系列截短的OmpATb蛋白的产生和表征表明，中央结构域（OmpATb73 - 220）足以在脂质双层中诱导天然蛋白的离子通道特性，即在1 M KCl中具有不对称插入、pH依赖性电压关闭、阳离子选择性和相似的电导值。蛋白质印迹分析表明，OmpATb的存在仅局限于某些致病物种。因此，天然OmpATb通道在低pH下关闭的倾向可能代表一种内在特性，使致病性分枝杆菌能够适应并在轻度酸性条件下存活，例如在巨噬细胞吞噬体中遇到的条件。
