Abstract
Mechanosensitive channels respond to mechanical forces exerted on the cell membrane and play vital roles in regulating the chemical equilibrium within cells and their environment. High-resolution structural information is required to understand the gating mechanisms of mechanosensitive channels. Protein-lipid interactions are essential for the structural and functional integrity of mechanosensitive channels, but detergents cannot maintain the crucial native lipid environment for purified mechanosensitive channels. Recently, detergent-free systems have emerged as alternatives for membrane protein structural biology. This report shows that while membrane-active polymer, SMA2000, could retain some native cell membrane lipids on the transmembrane domain of the mechanosensitive-like YnaI channel, the complete structure of the transmembrane domain of YnaI was not resolved. This reveals a significant limitation of SMA2000 or similar membrane-active copolymers. This limitation may come from the heterogeneity of the polymers and nonspecific interactions between the polymers and the relatively large hydrophobic pockets within the transmembrane domain of YnaI. However, this limitation offers development opportunities for detergent-free technology for challenging membrane proteins.
Highlights
Living organisms survive by relying on their adaptability to ever-changing environments
Similar to our previous study on AcrB, we found no evidence of ordered SMA copolymer molecules around the transmembrane domain
This is the case with AcrB, where we had reported a high-resolution single-particle cryo-EM structure of a lipid bilayer patch within the channel
Summary
Living organisms survive by relying on their adaptability to ever-changing environments. Many elegant mechanisms for adaptability have evolved in the long history of life on earth. Single-cell organisms such as bacteria often confront drastic osmolarity changes in their surroundings, leading to harmful turgor pressure changes on the bacterial cell membrane. Bacteria survival must keep the cell membrane turgor pressure in an acceptable range to avoid cell lysis [1,2,3]. It is well known that bacteria respond to this environmental change through mechanosensitive channels present on their cell membrane. Activation mechanisms of mechanosensitive channels at the atomic level are fundamental questions that remain incompletely understood
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