Molecular Mechanism of CCAAT-Enhancer Binding Protein Recruitment by the TRIB1 Pseudokinase
- Structure. 2015 Nov 3;23(11):2111-21. doi: 10.1016/j.str.2015.08.017.
- 1. The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC 3052, Australia; Department of Medical Biology, University of Melbourne, Parkville, VIC 3052, Australia.
- 2. Department of Microbiology and Immunology, Otago School of Medical Sciences, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
- 3. Biochemistry Department, Otago School of Medical Sciences, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
- 4. Biochemistry Department, Otago School of Medical Sciences, University of Otago, PO Box 56, Dunedin 9054, New Zealand. Electronic address: [email protected].
CCAAT-enhancer binding proteins (C/EBPs) are Transcription Factors that play a central role in the differentiation of myeloid cells and adipocytes. Tribbles Pseudokinases govern levels of C/EBPs by recruiting them to the COP1 ubiquitin Ligase for ubiquitination. Here, we present the first crystal structure of a Tribbles protein, which reveals a catalytically inactive TRIB1 pseudokinase domain with a unique adaptation in the αC helix. A second crystal structure and biophysical studies of TRIB1 with its C-terminal extension, which includes the COP1-binding motif, show that the C-terminal extension is sequestered at a site formed by the modified TRIB1 αC helix. In addition, we have identified and characterized the TRIB1 substrate-recognition sequence within C/EBPα, which is evolutionarily conserved in C/EBP Transcription Factors. Binding studies indicate that C/EBPα recruitment is weaker in the presence of the C-terminal COP1-binding motif, but the magnitude of this effect suggests that the two bind distinct rather directly overlapping binding sites.