FIGURE 14.

Intrinsic flexibility of the filament. (A) The proposed concertina movement of the octamer due to the opening and closing of the central SEPT3-group NC-interface. In this case, the twofold symmetry is preserved. (B) Flexion of the hexamer around the twofold axis between the two copies of SEPT7 at the center (yellow) present in the cryo-EM model (PDB:7M6J). The centre figure shows a linear particle which has a strict twofold axis perpendicular to the page (black lozenge). Above and below are shown bent particles. (C) Proposed flexion of the octamer, based on variations to the central NC-interface observed in crystal structures involving SEPT3-group members. In the central figure, the twofold axis is vertical (arrow). The upper complex is based on a central closed and shifted interface (PDB:6MQK) and the lower complex on the heterodimeric structure of SEPT7-SEPT3_T282Y (PDB:6UQQ).