The mechanosensitive channel of large conductance (MscL) from Mycobacterium tuberculosis has been used as a structural model for rationalizing functional observations in multiple MscL orthologs. Although these orthologs adopt similar structural architectures, they reportedly present significant functional differences. Subtle structural discrepancies on mechanosensitive channel nanopockets are known to affect mechanical gating and may be linked to large variability in tension sensitivity among these membrane channels. Here, we modify the nanopocket regions of MscL from Escherichia coli and M. tuberculosis and employ PELDOR/DEER distance and 3pESEEM deuterium accessibility measurements to interrogate channel structure within lipids, in which both channels adopt a closed conformation. Significant in-lipid structural differences between the two constructs suggest a more compact E. coli MscL at the membrane inner-leaflet, as a consequence of a rotated TM2 helix. Observed differences within lipids could explain E. coli MscL’s higher tension sensitivity and should be taken into account in extrapolated models used for MscL gating rationalization.

中文翻译：

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压敏域的脂质结构暗示机械敏感通道功能的多样性

来自结核分枝杆菌的大电导机械敏感通道 (MscL) 已被用作结构模型，用于合理化多个 MscL 直向同源物中的功能观察。尽管这些直向同源物采用相似的结构架构，但据报道它们存在显着的功能差异。已知机械敏感通道纳米袋上的细微结构差异会影响机械门控，并且可能与这些膜通道之间张力敏感性的巨大可变性有关。在这里，我们修改了来自大肠杆菌和结核分枝杆菌的 MscL 的纳米袋区域，并采用 PELDOR/DEER 距离和 3pESEEM 氘可及性测量来询问脂质内的通道结构，其中两个通道均采用封闭构象。两种构建体之间显着的脂质结构差异表明，由于 TM2 螺旋旋转，膜内叶处有更紧凑的大肠杆菌 MscL。观察到的脂质差异可以解释大肠杆菌 MscL 较高的张力敏感性，并且应在用于 MscL 门控合理化的外推模型中加以考虑。