Mouilleron Stephane, Guettler Sebastian, Langer Carola A, Treisman Richard, McDonald Neil Q
Structural Biology Laboratory, Cancer Research UK, London Research Institute, London, UK.
EMBO J. 2008 Dec 3;27(23):3198-208. doi: 10.1038/emboj.2008.235. Epub 2008 Nov 13.
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 RPEL(MAL) peptide:G-actin complexes. Both RPEL peptides bind to the G-actin hydrophobic cleft and to subdomain 3. These RPEL(MAL):G-actin structures explain the sequence conservation defining the RPEL motif, including the invariant arginine. Characterisation of the RPEL(MAL):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 RPEL(MAL) structures. Comparison with other actin-binding proteins reveals an unexpected similarity to the vitamin-D-binding protein, extending the G-actin-binding protein repertoire.
血清反应因子的转录活性通过与调节辅因子相互作用来控制，如共激活因子MAL/MRTF-A（心肌相关转录因子A）。MAL本身在体内受细胞肌动蛋白动力学变化的调节，这种变化会改变其与G-肌动蛋白的相互作用。MAL/MRTF-A的G-肌动蛋白传感机制位于其N端结构域，该结构域由三个串联的RPEL重复序列组成。我们描述了从两个独立的RPEL(MAL)肽:G-肌动蛋白复合物结构中获得的关于RPEL功能的首个分子见解。两个RPEL肽均与G-肌动蛋白疏水裂缝和亚结构域3结合。这些RPEL(MAL):G-肌动蛋白结构解释了定义RPEL基序的序列保守性，包括不变的精氨酸。通过荧光各向异性和基于细胞报告基因的分析对RPEL(MAL):G-肌动蛋白相互作用进行表征，证实了肌动蛋白结合残基对于MAL在体内正确定位和调节的重要性。我们确定了两种RPEL(MAL)结构在G-肌动蛋白结合方面的重要差异。与其他肌动蛋白结合蛋白的比较揭示了与维生素D结合蛋白的意外相似性，扩展了G-肌动蛋白结合蛋白库。
