Figure 5

Mobility and orientation of the MBP subunit.

(A) Plot showing the agreement between the 3D reconstruction and the MBP and GS crystal structures fitted into the map. Correlation coefficients between residues and the cryo-EM map were calculated at 8 Å resolution by program Phenix³⁴ and colored from red (CC ≤ 0.5) to blue (CC ≥ 0.9). (B) Plot of residue mobility predicted by normal mode analysis. Rms displacements calculated by program ElNemo⁵⁹ were scaled to have a mean value of 1 Å within the GS subunit and are plotted from blue (≤2 Å) to red (≥6 Å). (C) First vibrational normal mode of the MBP-GS Δ2 particle. Conformations are shown at phase values of +90^o (green) and −90^o (green) along the mode coordinate. Inset. Oscillation of the MBP subunit results in large displacements for residues distal from the junction and small displacements for proximal residues. Vibrational modes 1–6 are presented in Supplementary Video S3. (D) Cryo-EM map of the MBP-GS junction region. (E) Distortion of the helical junction region. The C-terminal helix of MBP fitted into the cryo-EM map (α16, magenta) deviates significantly from the orientation predicted by superimposing a helix with ideal geometry (beige) onto the N-terminal helix of GS (α1, cyan). (F) Orientation of the MBP subunit fitted into the cryo-EM map (magenta) compared to that predicted if the junction region had ideal helical geometry (beige).