title: Max-E47, a designed minimalist protein that targets the E-box DNA site in vivo and in vitro.
abstract: Max-E47 is a designed hybrid protein comprising the Max DNA-binding basic region and E47 HLH dimerization subdomain. In the yeast one-hybrid system (Y1H), Max-E47 shows strong transcriptional activation from the E-box site, 5'-CACGTG, targeted by the Myc/Max/Mad network of transcription factors; two mutants, Max-E47Y and Max-E47YF, activate more weakly from the E-box in the Y1H. Quantitative fluorescence anisotropy titrations to gain free energies of protein:DNA binding gave low nanomolar K(d) values for the native MaxbHLHZ, Max-E47, and the Y and YF mutants binding to the E-box site (14, 15, 9, and 6 nM, respectively), with no detectable binding to a nonspecific control duplex. Because these minimalist, E-box-binding hybrids have no activation domain and no interactions with the c-MycbHLHZ, as shown by the yeast two-hybrid assay, they can potentially serve as dominant-negative inhibitors that suppress activation of E-box-responsive genes targeted by transcription factors including the c-Myc/Max complex. As proof-of-principle, we used our modified Y1H, which allows direct competition between two proteins vying for a DNA target, to show that Max-E47 effectively outcompetes the native MaxbHLHZ for the E-box; weaker competition is observed from the two mutants, consistent with Y1H results. These hybrids provide a minimalist scaffold for further exploration of the relationship between protein structure and DNA-binding function and may have applications as protein therapeutics or biochemical probes capable of targeting the E-box site.
authors.affiliation: Department of Chemistry, University of Toronto, Mississauga, Ontario L5L 1C6, Canada.
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.forename: Antonia T
authors.initials: AT
authors.lastname: De Jong
authors.forename: S Hesam
authors.initials: SH
authors.lastname: Shahravan
authors.forename: Jumi A
authors.initials: JA
authors.lastname: Shin
mesh_terms: D000595:Amino Acid Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D024721:E-Box Elements; D005454:Fluorescence Polarization; D018257:Helix-Loop-Helix Motifs; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C106465:MNT protein, human; C116115:MYCBP protein, human; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D004247:DNA