Figure 4

Side chain interactions in the CDK12/CycK interface (a) Binding of the CDK12 β4-β5 loop to CycK. Shown is a superposition of the two complexes in the asymmetric unit of the CDK12^715–1052/CycK^11–267 structure (CDK12 chain A and CycK chain B are coloured green and light brown, respectively, whereas chains C and D are coloured gray). A structure-based sequence alignment (right panel) reveals the insertion in the β4-β5 loop of CDK12 and CDK13 as well as the sequence divergence across this region and the interacting H5 helix of CycK. The positions of displayed residues participating in hydrophobic (ϕ) and hydrogen bond (*) interactions are marked under the alignment. (b) Hydrophobic interactions define the core of the protein-protein interface. (c) Electrostatic interactions cluster outside the core interface.