Fig. 1.

Structure and pseudosymmetry of the protein-conducting channel SecY. a Left: Structure of the channel engaged by a secretory substrate: Geobacillus thermodenitrificans SecYE engaged by proOmpA (Protein Data Bank ID [PDB] 6itc). The cytoplasmic ATPase SecA is present in the model but not shown. Right: Rotated view of only the SecY N-half and substrate. b Pseudosymmetry of the N- and C-halves. Left: SecYE shown as tubes with the pseudo-C₂ symmetry axis denoted by a pointed oval. Right: Rotated view in ribbon representation. The N-half has been rotated 180° around the pseudo-C₂ symmetry axis and aligned to the C-half. SecE is divided where it intersects the symmetry axis into N-terminal (white) and C-terminal (grey) segments. A dashed black line indicates the same pseudo-C₂ symmetry axis shown at left after a 90° rotation. Stars indicate where the halves were split