Crystal structure of a complex between amino and carboxy terminal fragments of mDia1: insights into autoinhibition of diaphanous-related formins

PLoS One. 2010 Sep 30;5(9):e12992. doi: 10.1371/journal.pone.0012992.

Abstract

Formin proteins direct the nucleation and assembly of linear actin filaments in a variety of cellular processes using their conserved formin homology 2 (FH2) domain. Diaphanous-related formins (DRFs) are effectors of Rho-family GTPases, and in the absence of Rho activation they are maintained in an inactive state by intramolecular interactions between their regulatory N-terminal region and a C-terminal segment referred to as the DAD domain. Although structures are available for the isolated DAD segment in complex with the interacting region in the N-terminus, it remains unclear how this leads to inhibition of actin assembly by the FH2 domain. Here we describe the crystal structure of the N-terminal regulatory region of formin mDia1 in complex with a C-terminal fragment containing both the FH2 and DAD domains. In the crystal structure and in solution, these fragments form a tetrameric complex composed of two interlocking N+C dimers. Formation of the tetramer is likely a consequence of the particular N-terminal construct employed, as we show that a nearly full-length mDia1 protein is dimeric, as are other autoinhibited N+C complexes containing longer N-terminal fragments. The structure provides the first view of the intact C-terminus of a DRF, revealing the relationship of the DAD to the FH2 domain. Delineation of alternative dimeric N+C interactions within the tetramer provides two general models for autoinhibition in intact formins. In both models, engagement of the DAD by the N-terminus is incompatible with actin filament formation on the FH2, and in one model the actin binding surfaces of the FH2 domain are directly blocked by the N-terminus.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actins / chemistry
  • Actins / metabolism
  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Crystallography, X-Ray
  • Dimerization
  • Formins
  • Homeostasis*
  • Mice
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Multimerization
  • Protein Structure, Tertiary

Substances

  • Actins
  • Carrier Proteins
  • Diap1 protein, mouse
  • Formins