- Jamieson SA, Ruan Z, Burgess AE, Curry JR, McMillan HD, Brewster JL, Dunbier AK, Axtman AD, Kannan N, Mace PD
- Substrate binding allosterically relieves autoinhibition of the pseudokinase TRIB1.
- Sci Signal. 2018 Sep 25;11(549). pii: 11/549/eaau0597. doi:, 10.1126/scisignal.aau0597.
- The Tribbles family of pseudokinases recruits substrates to the ubiquitin ligase COP1 to facilitate ubiquitylation. CCAAT/enhancer-binding protein (C/EBP) family transcription factors are crucial Tribbles substrates in adipocyte and myeloid cell development. We found that the TRIB1 pseudokinase was able to recruit various C/EBP family members and that the binding of C/EBPbeta was attenuated by phosphorylation. To explain the mechanism of C/EBP recruitment, we solved the crystal structure of TRIB1 in complex with C/EBPalpha, which revealed that TRIB1 underwent a substantial conformational change relative to its substrate-free structure and bound C/EBPalpha in a pseudosubstrate-like manner. Crystallographic analysis and molecular dynamics and subsequent biochemical assays showed that C/EBP binding triggered allosteric changes that link substrate recruitment to COP1 binding. These findings offer a view of pseudokinase regulation with striking parallels to bona fide kinase regulation-by means of the activation loop and alphaC helix-and raise the possibility of small molecules targeting either the activation "loop-in" or "loop-out" conformations of Tribbles pseudokinases.