9h2v
a YnaI-MscS chimera in an open conformation purified in DDM showing ligand-filled pockets
Structural highlights
FunctionYNAI_ECOLI Mechanosensitive channel that protects cells against hypoosmotic stress when highly overexpressed.[1] MSCS_ECOLI Mechanosensitive channel that participates in the regulation of osmotic pressure changes within the cell, opening in response to stretch forces in the membrane lipid bilayer, without the need for other proteins. Forms an ion channel of 1.0 nanosiemens conductance with a slight preference for anions. The channel is sensitive to voltage; as the membrane is depolarized, less tension is required to open the channel and vice versa. The channel is characterized by short bursts of activity that last for a few seconds. The channel pore is formed by TM3 and the loop between TM2 and TM3. After a sharp turn at Gly-113, an alpha-helix (residues 114-127) is oriented nearly parallel to the plane of the putative lipid bilayer. On the intracellular side of the channel, the permeation pathway of MscS does not connect directly to the cytoplasm but instead opens to a large chamber that is connected to the cytoplasm. This chamber resembles a molecular filter that could serve to prescreen large molecules before they are allowed passage to the transmembrane pore. The TM1 and TM2 helices appear to be likely candidates for mediating the tension and voltage sensitivities of MscS. Gating requires large rearrangements of at least the C-terminus. Publication Abstract from PubMedOsmotically varying environments are challenging for bacterial cells. Sudden drops in osmolytes cause an increased membrane tension and rupture the cells in the absence of protective mechanisms. One family of protective proteins are mechanosensitive channels of small conductance that open in response to membrane tension. Although these channels have a common architecture, they vary widely in the number of transmembrane helices, conductivity, and gating characteristics. Although there are various structures of channels in the open and closed state, the underlying common principles of the gating mechanism remain poorly understood. Here we show that YnaI opens by radial relocation of the transmembrane sensor paddles together with a shortening of the pore, which contrasts the prototypic smaller MscS. A chimera of both channels with the YnaI sensor paddles and the pore containing C-terminal part of MscS is functional and has the tension response of the paddle donor. Our research shows that elements with different structural opening mechanisms can be mixed and matched within one channel as long as they support the common area expansion on the periplasmic side. Mechanosensitive channel engineering: A study on the mixing and matching of YnaI and MscS sensor paddles and pores.,Flegler VJ, Rasmussen A, Hedrich R, Rasmussen T, Bottcher B Nat Commun. 2025 Aug 23;16(1):7881. doi: 10.1038/s41467-025-63253-0. PMID:40849500[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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