title: Electrostatics at the membrane define MscL channel mechanosensitivity and kinetics.
abstract: The bacterial mechanosensitive channel of large conductance (MscL) serves as a biological emergency release valve, preventing the occurrence of cell lysis caused by acute osmotic stress. Its tractable nature allows it to serve as a paradigm for how a protein can directly sense membrane tension. Although much is known of the importance of the hydrophobicity of specific residues in channel gating, it has remained unclear whether electrostatics at the membrane plays any role. We studied MscL chimeras derived from functionally distinct orthologues: Escherichia coli and Staphylococcus aureus. Dissection of one set led to an observation that changing the charge of a single residue, K101, of E. coli (Ec)-MscL, effects a channel phenotype: when mutated to a negative residue, the channel is less mechanosensitive and has longer open dwell times. Assuming electrostatic interactions, we determined whether they are due to protein-protein or protein-lipid interactions by performing site-directed mutagenesis elsewhere in the protein and reconstituting channels into defined lipids, with and without negative head groups. We found that although both interactions appear to play some role, the primary determinant of the channel phenotype seems to be protein-lipid electrostatics. The data suggest a model for the role of electrostatic interactions in the dynamics of MscL gating.
authors.affiliation: Center for Translational Neurodegeneration and Regenerative Therapy, Shanghai Tenth People's Hospital, Tongji University School of Medicine, Shanghai, China; and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Dalian
authors.initials: D
authors.lastname: Zhong
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA paul.blount@utsouthwestern.edu.
authors.forename: Paul
authors.initials: P
authors.lastname: Blount
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D029968:Escherichia coli Proteins; D007473:Ion Channels; C086596:MscL protein, E coli
keywords: liposome reconstitution; mechanosensation; mechanosensory; protein–lipid interactions