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Co-Folding of a FliF-FliG Split Domain Forms the Basis of the MS:C Ring Interface within the Bacterial Flagellar Motor.

  • Author(s): Lynch, Michael J;
  • Levenson, Robert;
  • Kim, Eun A;
  • Sircar, Ria;
  • Blair, David F;
  • Dahlquist, Frederick W;
  • Crane, Brian R
  • et al.
Abstract

The interface between the membrane (MS) and cytoplasmic (C) rings of the bacterial flagellar motor couples torque generation to rotation within the membrane. The structure of the C-terminal helices of the integral membrane protein FliF (FliFC) bound to the N terminal domain of the switch complex protein FliG (FliGN) reveals that FliGN folds around FliFC to produce a topology that closely resembles both the middle and C-terminal domains of FliG. The interface is consistent with solution-state nuclear magnetic resonance, small-angle X-ray scattering, in vivo interaction studies, and cellular motility assays. Co-folding with FliFC induces substantial conformational changes in FliGN and suggests that FliF and FliG have the same stoichiometry within the rotor. Modeling the FliFC:FliGN complex into cryo-electron microscopy rotor density updates the architecture of the middle and upper switch complex and shows how domain shuffling of a conserved interaction module anchors the cytoplasmic rotor to the membrane.

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