Fig. 7: Comparison of T-loop phosphorylated and unphosphorylated Cdk7 structures.

a Superimposition of the crystal structure of T170 phosphorylated monomeric Cdk7 (PDB 1ua2; yellow)²⁹ with the doubly T-loop phosphorylated Cdk7 structure determined here (8pyr, blue). Despite T170 phosphorylation, Cdk7 adopts a completely different conformation of the T loop in the absence of Cyclin H and Mat1. b Overlay of the unphosphorylated CAK structure (8orm, sand)⁴⁷ with the doubly phosphorylated complex structure (8pyr). Only subtle differences exist in the positioning of the side chains, while the conformation of the T loop is largely unchanged. c Display of the electrostatic surface potential for the doubly phosphorylated CAK structure (8pyr). The phosphate groups of pS164 and pT170, each carrying two negative charges, oppose the basic residues and neutralize the surface charge. ATP•Mg²⁺ and the N-terminal residues 10-54 of Cdk7 were modelled into the CAK complex as described in Supplementary Fig. 3d. d The same view on the unphosphorylated CAK structure bound to the inhibitor THZ1 (8orm)⁴⁷ reveals an extended basic surface patch. The electrostatic surface charge is shown from −5 k_BT (red) to +5 k_BT (blue).