Domains 2 and 3 undergo massive rearrangement and refolding (Figure 2A,B) in the membrane-inserted form. The elongated two-stranded β-sheet of D2 rotates from its vertical position in the x-ray structure by 90° around a short glycine linker to an orientation parallel to the membrane plane in the pore complex. D2 connects D1 to D4, and its rotation results in a roughly linear translation of D1 by 35 Å towards the membrane surface and by 30 Å towards the pore centre. Otherwise, D2 required only minor adjustments of secondary structure for an optimal fit to the cryoEM map (Figures 1B and 2A, Figure 2—figure supplement 5).