Structural basis of actin filament nucleation and processive capping by a formin homology 2 domain

Nature. 2005 Feb 3;433(7025):488-94. doi: 10.1038/nature03251. Epub 2005 Jan 5.

Abstract

The conserved formin homology 2 (FH2) domain nucleates actin filaments and remains bound to the barbed end of the growing filament. Here we report the crystal structure of the yeast Bni1p FH2 domain in complex with tetramethylrhodamine-actin. Each of the two structural units in the FH2 dimer binds two actins in an orientation similar to that in an actin filament, suggesting that this structure could function as a filament nucleus. Biochemical properties of heterodimeric FH2 mutants suggest that the wild-type protein equilibrates between two bound states at the barbed end: one permitting monomer binding and the other permitting monomer dissociation. Interconversion between these states allows processive barbed-end polymerization and depolymerization in the presence of bound FH2 domain. Kinetic and/or thermodynamic differences in the conformational and binding equilibria can explain the variable activity of different FH2 domains as well as the effects of the actin-binding protein profilin on FH2 function.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actin Cytoskeleton / chemistry*
  • Actin Cytoskeleton / metabolism*
  • Actins / chemistry*
  • Actins / metabolism*
  • Amino Acid Sequence
  • Binding Sites
  • Crystallography, X-Ray
  • Dimerization
  • Kinetics
  • Microfilament Proteins / chemistry*
  • Microfilament Proteins / genetics
  • Microfilament Proteins / metabolism*
  • Models, Biological
  • Models, Molecular
  • Mutation / genetics
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Protein Structure, Quaternary
  • Protein Structure, Tertiary
  • Rhodamines / chemistry
  • Saccharomyces cerevisiae / chemistry*
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Structure-Activity Relationship
  • Thermodynamics

Substances

  • Actins
  • Bni1 protein, S cerevisiae
  • Microfilament Proteins
  • Peptide Fragments
  • Rhodamines
  • Saccharomyces cerevisiae Proteins
  • tetramethylrhodamine

Associated data

  • PDB/1Y64