Structural Basis of Membrane Protein Chaperoning through the Mitochondrial Intermembrane Space

Cell. 2018 Nov 15;175(5):1365-1379.e25. doi: 10.1016/j.cell.2018.10.039.


The exchange of metabolites between the mitochondrial matrix and the cytosol depends on β-barrel channels in the outer membrane and α-helical carrier proteins in the inner membrane. The essential translocase of the inner membrane (TIM) chaperones escort these proteins through the intermembrane space, but the structural and mechanistic details remain elusive. We have used an integrated structural biology approach to reveal the functional principle of TIM chaperones. Multiple clamp-like binding sites hold the mitochondrial membrane proteins in a translocation-competent elongated form, thus mimicking characteristics of co-translational membrane insertion. The bound preprotein undergoes conformational dynamics within the chaperone binding clefts, pointing to a multitude of dynamic local binding events. Mutations in these binding sites cause cell death or growth defects associated with impairment of carrier and β-barrel protein biogenesis. Our work reveals how a single mitochondrial "transfer-chaperone" system is able to guide α-helical and β-barrel membrane proteins in a "nascent chain-like" conformation through a ribosome-free compartment.

Keywords: NMR spectroscopy; TIM complex; binding by avidity; membrane protein; mitochondria; molecular dynamics simulation; protein import; protein translocation; small-angle X-ray scattering; transfer-chaperone.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Binding Sites
  • Intracellular Membranes / metabolism
  • Mitochondria / metabolism*
  • Mitochondrial Membrane Transport Proteins / chemistry
  • Mitochondrial Membrane Transport Proteins / genetics
  • Mitochondrial Membrane Transport Proteins / metabolism*
  • Molecular Chaperones / metabolism*
  • Molecular Dynamics Simulation
  • Mutagenesis, Site-Directed
  • Protein Binding
  • Protein Domains
  • Protein Precursors / chemistry
  • Protein Precursors / metabolism
  • Protein Structure, Secondary
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Alignment


  • Mitochondrial Membrane Transport Proteins
  • Molecular Chaperones
  • Protein Precursors
  • Saccharomyces cerevisiae Proteins