title: Structural changes in the mitochondrial Tim23 channel are coupled to the proton-motive force.
abstract: Tim23, the central subunit of the TIM23 protein-translocation complex, forms a voltage-gated channel in the mitochondrial inner membrane (MIM), an energy-conserving membrane that generates a proton-motive force to drive vital processes. Using high-resolution fluorescence mapping of a channel-facing transmembrane segment (TMS2) of Tim23 from Saccharomyces cerevisiae, we demonstrate that changes in the energized state of the MIM cause marked structural alterations in the channel region. In an energized membrane, TMS2 forms a continuous α-helix that is inaccessible to the aqueous intermembrane space (IMS). Upon depolarization, the helical periodicity of TMS2 is disrupted, and the channel becomes exposed to the IMS. Kinetic measurements confirm that changes in TMS2 conformation coincide with depolarization. These results reveal how the energized state of the membrane drives functionally relevant structural dynamics in membrane proteins coupled to processes such as channel gating.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut, USA.
authors.forename: Ketan
authors.initials: K
authors.lastname: Malhotra
authors.forename: Murugappan
authors.initials: M
authors.lastname: Sathappa
authors.forename: Judith S
authors.initials: JS
authors.lastname: Landin
authors.forename: Arthur E
authors.initials: AE
authors.lastname: Johnson
authors.forename: Nathan N
authors.initials: NN
authors.lastname: Alder
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D008856:Microscopy, Fluorescence; D051336:Mitochondrial Membranes / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D018892:Proton-Motive Force / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D046912:Multiprotein Complexes; D029701:Saccharomyces cerevisiae Proteins; C083081:TIM23 protein, S cerevisiae