Fig. 3: Both the BTB domain and the CUL3 N-terminal motif participate in dimeric CRL3^KLHL22 assembly.

a CRL3^KLHL22 dimer with the BTB domain enlarged. The cartoon model shows the core BTB fold (A1-A5, B1-B3), the 3-box (A6 and A7), and the inter-model swapped α1 and β1. BTB domain from protomer 1 and protomer 2 are colored yellow and orange, respectively. b, c Hydrophobic interactions mediate BTB dimer formation. Hydrophobic residues located within α1’ (b) and β1’ (c) from KLHL22 protomer 2 contact with hydrophobic residues from protomer 1 (shown in surface representation in the left panel). d Cryo-EM density map of the CUL3 NA motif (blue) interacts with KLHL22 (yellow). e Shown is a large area of interaction between the BTB domain of KLHL22 and the Η2, Η5, and Loop^H1-H2 of CUL3. The interaction is mainly mediated through polar interactions. f Hydrophobic core formed by the BTB domain of KLHL22 and the CR1 domain of CUL3. Inter-facial residues (Leu83 from KLHL22; Leu52, Phe54, Leu57, Ile122 from CUL3) are shown. g Overlay of CUL3 NA motif cartoon model (aa 14–24) on the density map. h The molecular interaction between CUL3 NA motif (aa 14–24) and KLHL22. i, j Cryo-EM density map of the CUL3 NA motif (blue) interacts with KLHL22 promoter 2 (orange). Overlay of CUL3 NA motif cartoon model on the density map (j). k Cryo-EM density map (EMD-37247) of the CUL3 NA motif (blue) interacts with KLHL22 promoter 2 (orange). l The molecular interaction between the CUL3 NA motif (aa 2–13) and the domain swapping β sheet of KLHL22. The interactions were revealed by 1 μs molecular dynamics simulation.