title: Structure of a pentavalent G-actin*MRTF-A complex reveals how G-actin controls nucleocytoplasmic shuttling of a transcriptional coactivator.
abstract: Subcellular localization of the actin-binding transcriptional coactivator MRTF-A is controlled by its interaction with monomeric actin (G-actin). Signal-induced decreases in G-actin concentration reduce MRTF-A nuclear export, leading to its nuclear accumulation, whereas artificial increases in G-actin concentration in resting cells block MRTF-A nuclear import, retaining it in the cytoplasm. This regulation is dependent on three actin-binding RPEL motifs in the regulatory domain of MRTF-A. We describe the structures of pentavalent and trivalent G-actin•RPEL domain complexes. In the pentavalent complex, each RPEL motif and the two intervening spacer sequences bound an actin monomer, forming a compact assembly. In contrast, the trivalent complex lacked the C-terminal spacer- and RPEL-actins, both of which bound only weakly in the pentavalent complex. Cytoplasmic localization of MRTF-A in unstimulated fibroblasts also required binding of G-actin to the spacer sequences. The bipartite MRTF-A nuclear localization sequence was buried in the pentameric assembly, explaining how increases in G-actin concentration prevent nuclear import of MRTF-A. Analyses of the pentavalent and trivalent complexes show how actin loads onto the RPEL domain and reveal a molecular mechanism by which actin can control the activity of one of its binding partners.
authors.affiliation: Structural Biology Group, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Mouilleron
authors.forename: Carola A
authors.initials: CA
authors.lastname: Langer
authors.forename: Sebastian
authors.initials: S
authors.lastname: Guettler
authors.forename: Neil Q
authors.initials: NQ
authors.lastname: McDonald
authors.forename: Richard
authors.initials: R
authors.lastname: Treisman
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D021581:Active Transport, Cell Nucleus; D020816:Amino Acid Motifs; D000818:Animals; D002467:Cell Nucleus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D041681:NIH 3T3 Cells; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; C511173:Mrtfa protein, mouse; D046912:Multiprotein Complexes; D015534:Trans-Activators