Extended Data Fig. 3: Fenestrations and C-linker in closed MthK.

a, b, Surface representation of MthK closed (a) and open (PDB 3LDC) (b) state transmembrane domains, coloured by amino acid hydrophobicity. The membrane boundaries are indicated. No fenestration was observed in the open state. c, d, A tunnel, drawn with HOLE, shows how fenestrations (drawn through only two opposing subunits) connect the lipid bilayer with the inside of the cavity (grey). e, The resolved C-linker domain and two extra helical turns of TM2 (blue) shown in one MthK subunit. f, Zoomed-in dashed square in e, showing direct interactions between residues in C-linker (blue) and the RCK N-lobe (green). The neighbouring subunit is in beige. The residues that may contribute to C-linker stabilization via hydrophobic and electrostatic interactions are indicated.