FIGURE 4.

Crystal structure of the SecYEβ complex in the resting state from Methanocaldococcus jannaschii [adapted from van den Berg et al. (2004) PDB: 1RHZ] (A). TM1-5 (red) and TM6-10 (cyan) are the halves of SecY. SecE and Sec61β are in yellow and purple, respectively. (B) The pore ring comprised of six residues (pink) and lateral gate (TM2b in red and TM7 in cyan) are highlighted. (C) The plug helix located above the pore ring is indicated in dark blue. (D) The SecYEβ complex from Thermus thermophiles (PDB: 5AWW). The lateral gate region comprised of TM2b (red) and TM7 (blue) is the site where the signal peptide or TM segments of membrane proteins exit the channel upon opening of the gate. The SecYEβ structures in (A–C) are shown perpendicular to the membrane.