FIGURE 7.

A, SDS-PAGE comparing truncated Rpn8(1–186)·Rpn11(1–229) and wild type heterodimer. B, DUB activity of truncated heterodimer was assessed on Lys¹¹-Ub₂. C, initial processing of Lys¹¹-Ub₂ plotted for truncated (red) and wild-type heterodimer (black). D, truncated heterodimer fails to process Lys⁴⁸-Ub₄ efficiently (top); however, it is competent to process Lys⁶³-Ub₄. E, structural alignment of full-length CSN5 (Protein Data Bank entry 4D10; cyan), truncated CSN5(1–257) (Protein Data Bank entry 4F7O; green), and truncated Rpn11(2–239) (Protein Data Bank entry 4O8X; purple) shows classical MPN motif coordinating the active site Zn²⁺ ion. Glu¹⁰⁴ (sticks) undergoes a 12-Å transition between the two forms of CSN5, regulating access to the Zn²⁺ ion in the process. Val⁷⁸ (purple sticks) of Rpn11 is the equivalent of Glu¹⁰⁴ in CSN5.