Mechanism of conditional partner selectivity in MITF/TFE family transcription factors with a conserved coiled coil stammer motif

• Published in: Nucleic acids research Vol. 48; no. 2; pp. 934 - 948
• Main Authors: Pogenberg, Vivian, Ballesteros-Álvarez, Josué, Schober, Romana, Sigvaldadóttir, Ingibjörg, Obarska-Kosinska, Agnieszka, Milewski, Morlin, Schindl, Rainer, Ögmundsdóttir, Margrét Helga, Steingrímsson, Eiríkur, Wilmanns, Matthias
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 24-01-2020
• Subjects: Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors - chemistry; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors - genetics; Cell Nucleus - chemistry; Ligands; Mice; Microphthalmia-Associated Transcription Factor - chemistry; Microphthalmia-Associated Transcription Factor - genetics; Protein Binding; Protein Conformation; Protein Domains - genetics; Protein Multimerization; Structural Biology
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gkz1104

Abstract
Interrupted dimeric coiled coil segments are found in a broad range of proteins and generally confer selective functional properties such as binding to specific ligands. However, there is only one documented case of a basic-helix–loop–helix leucine zipper transcription factor—microphthalmia-associated transcription factor (MITF)—in which an insertion of a three-residue stammer serves as a determinant of conditional partner selectivity. To unravel the molecular principles of this selectivity, we have analyzed the high-resolution structures of stammer-containing MITF and an engineered stammer-less MITF variant, which comprises an uninterrupted symmetric coiled coil. Despite this fundamental difference, both MITF structures reveal identical flanking in-phase coiled coil arrangements, gained by helical over-winding and local asymmetry in wild-type MITF across the stammer region. These conserved structural properties allow the maintenance of a proper functional readout in terms of nuclear localization and binding to specific DNA-response motifs regardless of the presence of the stammer. By contrast, MITF heterodimer formation with other bHLH-Zip transcription factors is only permissive when both factors contain either the same type of inserted stammer or no insert. Our data illustrate a unique principle of conditional partner selectivity within the wide arsenal of transcription factors with specific partner-dependent functional readouts.