Figure 3. UtpB has an elongated structure with a mobile globular domain on one end.

(a) Representative ISAC³⁰ 2D class averages showing a tetrameric elongated body with a highly mobile domain that can sample a large range of conformations. (b) Comparative ISAC 2D class averages of endogenous UtpB and of recombinant UtpB lacking Utp6 and Utp18. (c) Different views of a random conical tilt reconstruction of UtpB (EMD-8223) show the elongated structure of the tetrameric core and weak density for the flexible domain at the tip of the foot. The manually docked double-β-propeller of Utp21 (pdb code 4nsx (ref. ¹⁶)) is shown as cartoon representation in red in the foot region of UtpB.