4agf
MTSSL spin labeled L124C mutant of MscS in the open form
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 heptameric mechanosensitive channel of small conductance (MscS) provides a critical function in Escherichia coli where it opens in response to increased bilayer tension. Three approaches have defined different closed and open structures of the channel, resulting in mutually incompatible models of gating. We have attached spin labels to cysteine mutants on key secondary structural elements specifically chosen to discriminate between the competing models. The resulting pulsed electron-electron double resonance (PELDOR) spectra matched predicted distance distributions for the open crystal structure of MscS. The fit for the predictions by structural models of MscS derived by other techniques was not convincing. The assignment of MscS as open in detergent by PELDOR was unexpected but is supported by two crystal structures of spin-labeled MscS. PELDOR is therefore shown to be a powerful experimental tool to interrogate the conformation of transmembrane regions of integral membrane proteins. Conformational state of the MscS mechanosensitive channel in solution revealed by pulsed electron-electron double resonance (PELDOR) spectroscopy.,Pliotas C, Ward R, Branigan E, Rasmussen A, Hagelueken G, Huang H, Black SS, Booth IR, Schiemann O, Naismith JH Proc Natl Acad Sci U S A. 2012 Oct 2;109(40):E2675-82. doi:, 10.1073/pnas.1202286109. Epub 2012 Sep 10. PMID:23012406[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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