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. Epub 2015 Oct 9.

Abstract

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.

Keywords: C/EBP; CCAAT-enhancer binding protein; COP1; Constitutive Photomorphogenesis Protein 1; DFG motif; Kinase; Pseudokinase; TRIB1; Tribbles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Binding Sites
  • CCAAT-Enhancer-Binding Protein-alpha / chemistry
  • CCAAT-Enhancer-Binding Protein-alpha / metabolism*
  • Enhancer Elements, Genetic*
  • Humans
  • Intracellular Signaling Peptides and Proteins / chemistry*
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Molecular Sequence Data
  • Protein Binding
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*
  • Protein-Serine-Threonine Kinases / chemistry
  • Protein-Serine-Threonine Kinases / metabolism

Substances

  • CCAAT-Enhancer-Binding Protein-alpha
  • Intracellular Signaling Peptides and Proteins
  • TRIB1 protein, human
  • Protein-Serine-Threonine Kinases