Structurally distinct modes of recognition of the KIX domain of CBP by Jun and CREB.

Gene expression is coordinated in part by interactions between transcriptional activators and other transcription factors such as coactivators. The KIX domain of the coactivator and histone acetyltransferase CREB binding protein (CBP) binds numerous mammalian and viral transcriptional activators such as BRCA1, CREB, c-Jun, c-Myb, p53, papillomavirus E2, and HTLV-1 Tax. Formation of the CREB-CBP complex depends on phosphorylation of the KID region of CREB and involves induced folding of KID upon binding a hydrophobic groove of the KIX domain of CBP. Here we investigate the formation of the complex formed by human KIX and the N-terminal activation domain of human c-Jun. The c-Jun activation domain and KID do not share significant sequence similarity. Circular dichroism spectroscopy shows that the Jun N-terminal activation domain is intrinsically disordered in isolation and that KIX binding is independent of Jun phosphorylation. In contrast to the mode of binding exhibited by CREB, NMR chemical shift mapping indicates that the c-Jun activation domain binds to a distinctly different surface of KIX than used by CREB. Moreover, NMR and sedimentation equilibrium studies show that the activation domains of c-Jun and CREB can simultaneously bind the KIX domain of CBP. The results illustrate a new mode of binding and combinatorial recruitment via the KIX domain of CBP by multiple transcriptional activators.