Figure 4. Interaction of β₂ with α₆ rings.

(A) ISAC averages of negatively stained α with β in the presence of both 3 mM ATP and 0.05 mM dATP (same concentrations used for cryo-EM structure) reveal variability in both occupancy and location of β. Bottom row presents corresponding views of the α₆ ring as a low-resolution surface with circles highlighting the position of β₂ in the averages. (B) Similar views seen in ISAC averages from cryo-EM specimens of α with β and ClFTP. (C) 3D cryo-EM reconstruction of α with β and ClFTP. (D) Model of β₂ docked with an α₂ in the α₆ ring is tightly constrained by proximity of cone domains (green) and the three-helix insertion (purple) of α₂ and adjacent α subunits in the ring. (E) Variance map shows additional partially ordered density for C-terminal tails of α protruding into the central opening of the α₆ ring.