Structural Characterization of the DAXX N-Terminal Helical Bundle Domain and Its Complex with Rassf1C

SummaryDAXX is a scaffold protein with diverse roles including transcription and cell cycle regulation. Using NMR spectroscopy, we demonstrate that the C-terminal half of DAXX is intrinsically disordered, whereas a folded domain is present near its N terminus. This domain forms a left-handed four-helix bundle (H1, H2, H4, H5). However, due to a crossover helix (H3), this topology differs from that of the Sin3 PAH domain, which to date has been used as a model for DAXX. The N-terminal residues of the tumor suppressor Rassf1C fold into an amphipathic α helix upon binding this DAXX domain via a shallow cleft along the flexible helices H2 and H5 (KD ∼60 μM). Based on a proposed DAXX recognition motif as hydrophobic residues preceded by negatively charged groups, we found that peptide models of p53 and Mdm2 also bound the helical bundle. These data provide a structural foundation for understanding the diverse functions of DAXX.

Graphical AbstractFigure optionsDownload high-quality image (158 K)Download as PowerPoint slideHighlights
► The modular structure of human DAXX was characterized
► DAXX contains a left-handed helical bundle, distinct from the Sin3 PAH domain
► Rassf1C undergoes a coil-to-helix transition upon binding the DAXX helical bundle
► A DAXX recognition motif contains hydrophobic and flanking acidic residues