Structure of a Pentavalent G-Actin•MRTF-A Complex Reveals How G-Actin Controls Nucleocytoplasmic Shuttling of a Transcriptional Coactivator

Sci. Signal., 14 June 2011
Vol. 4, Issue 177, p. ra40
DOI: 10.1126/scisignal.2001750

Structure of a Pentavalent G-Actin•MRTF-A Complex Reveals How G-Actin Controls Nucleocytoplasmic Shuttling of a Transcriptional Coactivator

  1. Stéphane Mouilleron1,
  2. Carola A. Langer2,*,
  3. Sebastian Guettler2,*,,
  4. Neil Q. McDonald1,3,, and
  5. Richard Treisman2,
  1. 1Structural Biology Group, Cancer Research UK London Research Institute, Lincoln’s Inn Fields Laboratories, 44 Lincoln’s Inn Fields, London WC2A 3LY, UK.
  2. 2Transcription Group, Cancer Research UK London Research Institute, Lincoln’s Inn Fields Laboratories, London WC2A 3LY, UK.
  3. 3Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK.
  1. To whom correspondence should be addressed. E-mail: Neil.McDonald{at}cancer.org.uk (N.Q.M.); Richard.Treisman{at}cancer.org.uk (R.T.)
  • * These authors contributed equally to this work.

  • Present address: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario M5G 1X5, Canada.

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.

Citation:

S. Mouilleron, C. A. Langer, S. Guettler, N. Q. McDonald, and R. Treisman, Structure of a Pentavalent G-Actin•MRTF-A Complex Reveals How G-Actin Controls Nucleocytoplasmic Shuttling of a Transcriptional Coactivator. Sci. Signal. 4, ra40 (2011).

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