title: The mechanosensitive channel of small conductance (MscS) functions as a Jack-in-the box.
abstract: Phenotypical analysis of the lipid interacting residues in the closed state of the mechanosensitive channel of small conductance (MscS) from Escherichia coli (E. coli) has previously shown that these residues are critical for channel function. In the closed state, mutation of individual hydrophobic lipid lining residues to alanine, thus reducing the hydrophobicity, resulted in phenotypic changes that were observable using in vivo assays. Here, in an analogous set of experiments, we identify eleven residues in the first transmembrane domain of the open state of MscS that interact with the lipid bilayer. Each of these residues was mutated to alanine and leucine to modulate their hydrophobic interaction with the lipid tail-groups in the open state. The effects of these changes on channel function were analyzed using in vivo bacterial assays and patch clamp electrophysiology. Mutant channels were found to be functionally indistinguishable from wildtype MscS. Thus, mutation of open-state lipid interacting residues does not differentially stabilize or destabilize the open, closed, intermediate, or transition states of MscS. Based on these results and other data from the literature, we propose a new gating paradigm for MscS where MscS acts as a "Jack-In-The-Box" with the intrinsic bilayer lateral pressure holding the channel in the closed state. In this model, upon application of extrinsic tension the channel springs into the open state due to relief of the intrinsic lipid bilayer pressure.
authors.affiliation: Department of Chemistry, Washington University in St. Louis, MO 63130, USA; Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 76390, USA.
authors.forename: Hannah R
authors.initials: HR
authors.lastname: Malcolm
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 76390, USA. Electronic address: paul.blount@utsouthwestern.edu.
authors.forename: Paul
authors.initials: P
authors.lastname: Blount
authors.affiliation: Department of Chemistry, Washington University in St. Louis, MO 63130, USA. Electronic address: Joshua.Maurer@att.net.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Maurer
mesh_terms: D001665:Binding Sites / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology*; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D040542:Mechanotransduction, Cellular / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D008958:Models, Molecular; D009154:Mutation; D018408:Patch-Clamp Techniques; D011312:Pressure; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013104:Spheroplasts / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D029968:Escherichia coli Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; C469542:MscS protein, E coli
keywords: Bacterial ion channel; Gating mechanism; Jack-In-The-Box; Lipid interaction; Mechanosensitive channel of small conductance (MscS)