Fig. 1.

Helical crystallization of the Syt1^C2AB–SNARE complex on the lipid membrane surface. a Cryo-electron micrograph of the Syt1^C2AB–SNARE complex helically organized on lipid nanotubes. A representative micrograph of ~41 nm protein-coated LNTs with homogenous helical packing used in the reconstruction is shown. b Corresponding Fourier Transform of the LNTs shows a helical diffraction pattern with the Bessel functions for basis vectors, which corresponds to Δz = 7.35 A Δφ = 78.48; 14,−4 start helix. c Iso-surface representation of the helical reconstruction of protein-coated LNTs at 10.4 Å resolution. The Syt1^C2AB-SNARE protein (blue) is arranged on the lipid bilayer tube (yellow) with characteristic rod-like densities (magenta) corresponding to the SNARE complex oriented almost parallel to the tube axis and thus, locally experience a relatively flat bilayer surface. d Grayscale density slice through the one side of the 3D-volume along the helical axis (top, slice depth 1) and quarter grayscale slice from cross-sectional density (bottom, slice depth 30). The densities corresponding to α-helices forming the SNAREpin (red arrow), as well with phospholipid heads plane of the inner (i) and outer (o) membrane leaflets are also well defined