title: MDMX contains an autoinhibitory sequence element.
abstract: MDM2 and MDMX are homologous proteins that bind to p53 and regulate its activity. Both contain three folded domains and ~70% intrinsically disordered regions. Previous detailed structural and biophysical studies have concentrated on the isolated folded domains. The N-terminal domains of both exhibit high affinity for the disordered N-terminal of p53 (p53TAD) and inhibit its transactivation function. Here, we have studied full-length MDMX and found a ~100-fold weaker affinity for p53TAD than does its isolated N-terminal domain. We found from NMR spectroscopy and binding studies that MDMX (but not MDM2) contains a conserved, disordered self-inhibitory element that competes intramolecularly for binding with p53TAD. This motif, which we call the WWW element, is centered around residues Trp200 and Trp201. Deletion or mutation of the element increased binding affinity of MDMX to that of the isolated N-terminal domain level. The self-inhibition of MDMX implies a regulatory, allosteric mechanism of its activity. MDMX rests in a latent state in which its binding activity with p53TAD is masked by autoinhibition. Activation of MDMX would require binding to a regulatory protein. The inhibitory function of the WWW element may explain the oncogenic effects of an alternative splicing variant of MDMX that does not contain the WWW element and is found in some aggressive cancers.
authors.affiliation: Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
authors.forename: Michal
authors.initials: M
authors.lastname: Bista
authors.forename: Miriana
authors.initials: M
authors.lastname: Petrovich
authors.forename: Alan R
authors.initials: AR
authors.lastname: Fersht
mesh_terms: D002151:Calorimetry; D018797:Cell Cycle Proteins; D002850:Chromatography, Gel; D006801:Humans; D019906:Nuclear Magnetic Resonance, Biomolecular; D009687:Nuclear Proteins / Q000235:genetics*; D009857:Oncogenes / Q000235:genetics*; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors* / Q000235:genetics; D054875:Ubiquitination; D014461:Ultracentrifugation
chemical_list: D018797:Cell Cycle Proteins; C482775:MDM4 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53
keywords: HDMX; IDP; MDM4; MDMX-S; TROSY