Fig. 2. 3D structure of the -secretase complex. (A) Surface rendering of the 3D reconstruction. The first row displays side views generated by rotation around a vertical axis, the second row shows tilted views generated by rotation around a horizontal axis. The rotation angles are shown within each view. Two openings at the top and bottom are labelled H1 and H2, respectively, where visible. The top density is labelled NCT because lectin labelling showed that the NCT ectodomain is located at this surface (Lazarov et al., 2006). (B) The potential transmembrane segment has a belt-like structure and is indicated by two parallel dashed lines, 60 Å apart. For size comparison, a typical transmembrane -helix, taken from the rhodopsin structure (protein data bank ID code 1GZM), is shown to the left of the structure. (C) A cut-open view of the -secretase complex, revealing a large central chamber and one opening at the top (H1) and one at the bottom (H2). Two weak-density lateral regions are labelled with asterisks. Reproduced from Lazarov et al. PNAS, 103(18), 6889-6894, 2006 with permission [Copyright (2006) National Academy of Sciences, USA].