Figure 1.

Cuboctahedron of the 24-subunit YfbU particle and noncrystallographic symmetry averaging. (a) YfbU forms a 24-subunit particle with cuboctahedral P432 point symmetry and the particle sits on the crystallographic threefold axis. The vertices represent the binding sites for the W₁₂ cluster at the twofold-related interface of two subunits from which we derived initial NCS matrices. (b) Two tetramers within each particle are independent subunits in the half asymmetric unit. (c) Two particles in the asymmetric unit with four independent tetramers (shaded planes). Unit-cell edges are shown as thin yellow sticks, crystallographic dyads in green, crystallographic threefold axes in red and cuboctahedron symmetry as thick yellow sticks. (d) Noncrystallographic symmetry real-space electron-density averaging statistics in the first (filled) and fourth pass (open) after mask editing with the highest resolutions from 10 to 2.5 Å resolution in 20 steps with ten cycles of refinement at each resolution. Both R factors (black and green) and electron-density correlation coefficients (red and blue) are plotted.