Extended Data Figure 7. Localization of signal sequences in the G. thermodenitrificans SecY and mammalian Sec61 channels and of a TM domain in the mammalian Sec61 channel.

a, In the active channel (salmon), the signal sequence displaces TM7 and TM8 in the idle T. thermophilus channel (cyan). b, As in a, but comparison with the idle M. jannaschii channel (tan). The C-region of the signal sequence takes the position of TM7. c, Side view of the interactions of the H-region of the signal sequence with TM2 of G. thermodenitrificans SecY. Interacting amino acids are indicated. d, Stereo view showing the intercalation of the C-region into the periplasmic side of the lateral gate. Residues of the amphipathic helix are indicated. e, The active G. thermodenitrificans channel (in salmon) was aligned with a mammalian channel (in grey) containing a nascent membrane protein (PDB ID: 4CG6) using secondary structure matching ⁴⁷. The signal sequence in the bacterial channel is shown in green, and the TM segment of the nascent membrane protein in yellow. f, As in e, but comparison of the active G. thermodenitrificans channel with a mammalian Sec61 channel (light blue) containing a secretory protein fragment (PDB ID 3JC2). The signal sequences are shown in green and yellow, respectively.