Fig. 4.

Cyclin A2 engages APC/C^Cdc20 with two binding modes. a Cryo-EM reconstruction of the constitutive active mutant APC/C^ΔApc1-300s in complex with Cdc20 and Cdk2-cyclinA2-Cks2 at 3.2 Å resolution, with the D2 box and KEN box density highlighted in orange, Cdc20 in purple and Apc10 in blue. Individual chains of the APC/C^Cdc20-Hsl1 structure were fitted into the EM density (PDB 5G04⁴⁸). Coordinates for Cdc20, Apc10 and the D2 box and KEN box of cyclin A2 are coloured according to the density, with the remaining APC/C subunits in grey. b Close-up view of the degron-binding site when the D2 box occupies the D-box binding site. No densities corresponding to the ABBA motif could be found in its binding pocket (dashed black line). c Close-up view of the degron-binding site when the ΔD1 mutant was used as a substrate which closely resembles the D2 box class of the wild-type structure. d Close-up view of the degron-binding site in the D1 box class when wild-type Cdk2-cyclinA2-Cks2 was used as a substrate reveals that the D1 box binds to APC/C^Cdc20 in cooperation with the KEN box and ABBA motif. e Superposition of the D1 box and D2 box classes on Apc10 revealed a large movement of Cdc20^WD40. The D1 box is depicted in orange while the D2 box in yellow. Cdc20^WD40 from the D1 box class is in dark purple, while that of the D2 box class in pale purple. f Superposition of the two classes on Cdc20^WD40 showed that the D2 box overlaps well with the N-terminal region of the D1 box, yet the C-terminal segment of the D1 box folds back with a kink to be sandwiched between Cdc20^WD40 and Apc10. g Superposition of the cyclin A2 D2 box structure with the structure of the canonical D box of Hsl1 (PDB 5G04⁴⁸). h–j Schematic cartoon showing the two different binding modes of cyclin A2 to APC/C^Cdc20. k Ubiquitination assay showing different ubiquitination efficiency of the two binding modes of cyclin A2 to APC/C^Cdc20. Source data are provided as a Source Data file