title: Restricted leucine zipper dimerization and specificity of DNA recognition of the melanocyte master regulator MITF.
abstract: Microphthalmia-associated transcription factor (MITF) is a master regulator of melanocyte development and an important oncogene in melanoma. MITF heterodimeric assembly with related basic helix-loop-helix leucine zipper transcription factors is highly restricted, and its binding profile to cognate DNA sequences is distinct. Here, we determined the crystal structure of MITF in its apo conformation and in the presence of two related DNA response elements, the E-box and M-box. In addition, we investigated mouse and human Mitf mutations to dissect the functional significance of structural features. Owing to an unusual three-residue shift in the leucine zipper register, the MITF homodimer shows a marked kink in one of the two zipper helices to allow an out-of-register assembly. Removal of this insertion relieves restricted heterodimerization by MITF and permits assembly with the transcription factor MAX. Binding of MITF to the M-box motif is mediated by an unusual nonpolar interaction by Ile212, a residue that is mutated in mice and humans with Waardenburg syndrome. As several related transcription factors have low affinity for the M-box sequence, our analysis unravels how these proteins discriminate between similar target sequences. Our data provide a rational basis for targeting MITF in the treatment of important hereditary diseases and cancer.
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, 22603 Hamburg, Germany.
authors.forename: Vivian
authors.initials: V
authors.lastname: Pogenberg
authors.forename: Margrét H
authors.initials: MH
authors.lastname: Ogmundsdóttir
authors.forename: Kristín
authors.initials: K
authors.lastname: Bergsteinsdóttir
authors.forename: Alexander
authors.initials: A
authors.lastname: Schepsky
authors.forename: Bengt
authors.initials: B
authors.lastname: Phung
authors.forename: Viktor
authors.initials: V
authors.lastname: Deineko
authors.forename: Morlin
authors.initials: M
authors.lastname: Milewski
authors.forename: Eiríkur
authors.initials: E
authors.lastname: Steingrímsson
authors.forename: Matthias
authors.initials: M
authors.lastname: Wilmanns
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004742:Enhancer Elements, Genetic / Q000235:genetics; D006801:Humans; D016350:Leucine Zippers / Q000235:genetics; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014849:Waardenburg Syndrome / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D051739:Microphthalmia-Associated Transcription Factor