HSP90-CDC37-PP5 forms a structural platform for kinase dephosphorylation

A Experimental cryoEM map of HSP90–CDC37–BRAFV600E complex, surface coloured according to the underlying protein chain. The HSP90 dimer (blue and yellow—the colours of the Ukrainian flag) is in a closed conformation, with CDC37 (pink) wrapping around the edge of one of the HSP90 monomers. The C-lobe of the kinase domain of BRAFV600E (orange) packs against the opposite face to the globular C-terminal half of CDC37, and interacts with the N-terminal coiled-coil α-hairpin of CDC37. This and all other molecular graphics were created using ChimeraX. B ATP (or possibly ADP-molybdate) molecules (green bonds) are bound in the N-terminal domain of both HSP90 monomers and interact with the catalytic Arg392 from the middle domain. C Phosphorylated Ser13 of CDC37 interacts with His33 and Arg36 of CDC37, stabilising the conformation of the N-terminal part of CDC37 and bridging to Lys406 from the middle segment of one of the HSP90 monomers. D The bound BRAFV600E is well resolved throughout, allowing for a nearly full tracing of its amino acid sequence in the cryoEM map. E Within the complex, Trp31 displaces Phe595 of the key regulatory DFG motif into a different conformation than in the intact kinase, stabilised by the interaction of DFG Asp594 with CDC37 Arg30. This conformational switch is facilitated by the oncogenic V600E mutation in the ‘activation segment’ immediately following the DFG motif, and explains why the oncogenic BRAFV600E mutant is a strong client of the HSP90-CDC37 chaperone system, whereas the wild-type is not. F HSP90 itself only makes peripheral contact with the kinase C-lobe, but mutation of the HSP90 residues involved impairs kinase activation in vivo. G As previously seen for CDK4 in complex with HSP90 and CDC37, the strand from the kinase N-lobe immediately upstream of the well-ordered C-lobe, becomes linearised and stretches between the two HSP90 monomers to emerge on the other face of the complex adjacent to the globular part of CDC37. No ordered structure upstream of this is visible in the cryoEM maps.