Molecular basis for G-actin binding to RPEL motifs from the serum response factor coactivator MAL

• Stephane Mouilleron ^[1] ; Sebastian Guettler ^[1] ; Carola A Langer ^[1] ; Richard Treisman ^[1] ; Neil Q McDonald ^[1]
  1. [1] London Research Institute

     London Research Institute

     Reino Unido

     
• Localización: EMBO journal: European Molecular Biology Organization, ISSN 0261-4189, Vol. 27, Nº. 23, 2008, págs. 3198-3208
• Idioma: inglés
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• Resumen

  • Serum response factor transcriptional activity is controlled through interactions with regulatory cofactors such as the coactivator MAL/MRTF-A (myocardin-related transcription factor A). MAL is itself regulated in vivo by changes in cellular actin dynamics, which alter its interaction with G-actin. The G-actin-sensing mechanism of MAL/MRTF-A resides in its N-terminal domain, which consists of three tandem RPEL repeats. We describe the first molecular insights into RPEL function obtained from structures of two independent RPELMAL peptide:G-actin complexes. Both RPEL peptides bind to the G-actin hydrophobic cleft and to subdomain 3. These RPELMAL:G-actin structures explain the sequence conservation defining the RPEL motif, including the invariant arginine. Characterisation of the RPELMAL:G-actin interaction by fluorescence anisotropy and cell reporter-based assays validates the significance of actin-binding residues for proper MAL localisation and regulation in vivo. We identify important differences in G-actin engagement between the two RPELMAL structures. Comparison with other actin-binding proteins reveals an unexpected similarity to the vitamin-D-binding protein, extending the G-actin-binding protein repertoire.