7oo0
Mechanosensitive channel MscS solubilized with DDM in open conformation
Structural highlights
FunctionMSCS_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 PubMedThe mechanosensitive channel of small conductance (MscS) protects bacteria against hypoosmotic shock. It can sense the tension in the surrounding membrane and releases solutes if the pressure in the cell is getting too high. The membrane contacts MscS at sensor paddles, but lipids also leave the membrane and move along grooves between the paddles to reside as far as 15 A away from the membrane in hydrophobic pockets. One sensing model suggests that a higher tension pulls lipids from the grooves back to the membrane, which triggers gating. However, it is still unclear to what degree this model accounts for sensing and what contribution the direct interaction of the membrane with the channel has. Here, we show that MscS opens when it is sufficiently delipidated by incubation with the detergent dodecyl-beta-maltoside or the branched detergent lauryl maltose neopentyl glycol. After addition of detergent-solubilized lipids, it closes again. These results support the model that lipid extrusion causes gating: Lipids are slowly removed from the grooves and pockets by the incubation with detergent, which triggers opening. Addition of lipids in micelles allows lipids to migrate back into the pockets, which closes the channel even in the absence of a membrane. Based on the distribution of the aliphatic chains in the open and closed conformation, we propose that during gating, lipids leave the complex on the cytosolic leaflet at the height of highest lateral tension, while on the periplasmic side, lipids flow into gaps, which open between transmembrane helices. Mechanosensitive channel gating by delipidation.,Flegler VJ, Rasmussen A, Borbil K, Boten L, Chen HA, Deinlein H, Halang J, Hellmanzik K, Loffler J, Schmidt V, Makbul C, Kraft C, Hedrich R, Rasmussen T, Bottcher B Proc Natl Acad Sci U S A. 2021 Aug 17;118(33):e2107095118. doi: , 10.1073/pnas.2107095118. PMID:34376558[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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