Ernst Ruska Prize 2017Cryo-EM structure of haemoglobin at 3.2 Å determined with the Volta phase plate

Figure 1. Phase plate imaging of 64 kDa Hgb. (a) Electron micrograph of metHgb recorded at ∼500 nm underfocus with the Volta phase plate (VPP) (scale bar, 30 nm). (b) Power spectrum of the image in a, featuring contrast transfer function (CTF) Thon rings permitting defocus and phase shift estimation. (c) The 2D class averages of Hgb showing secondary structure elements in projection. (d) Reconstructed 3D electron scattering potential map and model of Hgb. (e) VPP reconstruction fitted with three conformers of Hgb present in crystal structure PDB 4N7O. The reconstructed 3D map agrees best with chains A–D of PDB 4N7O representing the R2 state of Hgb.