Abstract
Phosphatidylinositol 3-kinase-related protein kinases (PIKKs) play critical roles in various metabolic pathways related to cell proliferation and survival. The TELO2-TTI1-TTI2 (TTT) complex has been proposed to recognize newly synthesized PIKKs and to deliver them to the R2TP complex (RUVBL1-RUVBL2-RPAP3-PIH1D1) and the heat shock protein 90 chaperone, thereby supporting their folding and assembly. Here, we determined the cryo-EM structure of the TTT complex at an average resolution of 4.2 Å. We describe the full-length structures of TTI1 and TELO2, and a partial structure of TTI2. All three proteins form elongated helical repeat structures. TTI1 provides a platform on which TELO2 and TTI2 bind to its central region and C-terminal end, respectively. The TELO2 C-terminal domain (CTD) is required for the interaction with TTI1 and recruitment of Ataxia-telangiectasia mutated (ATM). The N- and C-terminal segments of TTI1 recognize the FRAP-ATM-TRRAP (FAT) domain and the N-terminal HEAT repeats of ATM, respectively. The TELO2 CTD and TTI1 N- and C-terminal segments are required for cell survival in response to ionizing radiation.