2.4 Å resolution crystal structure of human TRAP1NM, the Hsp90 paralog in the mitochondrial matrix

TRAP1 is an organelle-specific Hsp90 paralog that is essential for neoplastic growth. As a member of the Hsp90 family, TRAP1 is presumed to be a general chaperone facilitating the late-stage folding of Hsp90 client proteins in the mitochondrial matrix. Interestingly, TRAP1 cannot replace cytosolic Hsp90 in protein folding, and none of the known Hsp90 co-chaperones are found in mitochondria. Thus, the three-dimensional structure of TRAP1 must feature regulatory elements that are essential to the ATPase activity and chaperone function of TRAP1. Here, the crystal structure of a human TRAP1(NM) dimer is presented, featuring an intact N-domain and M-domain structure, bound to adenosine 5'-beta,gamma-imidotriphosphate (ADPNP). The crystal structure together with epitope-mapping results shows that the TRAP1 M-domain loop 1 contacts the neighboring subunit and forms a previously unobserved third dimer interface that mediates the specific interaction with mitochondrial Hsp70.