title: The formin DAD domain plays dual roles in autoinhibition and actin nucleation.
abstract: Formins are a large family of actin assembly-promoting proteins with many important biological roles. However, it has remained unclear how formins nucleate actin polymerization. All other nucleators are known to recruit actin monomers as a central part of their mechanisms. However, the actin-nucleating FH2 domain of formins lacks appreciable affinity for monomeric actin. Here, we found that yeast and mammalian formins bind actin monomers but that this activity requires their C-terminal DAD domains. Furthermore, we observed that the DAD works in concert with the FH2 to enhance nucleation without affecting the rate of filament elongation. We dissected this mechanism in mDia1, mapped nucleation activity to conserved residues in the DAD, and demonstrated that DAD roles in nucleation and autoinhibition are separable. Furthermore, DAD enhancement of nucleation was independent of contributions from the FH1 domain to nucleation. Together, our data show that (1) the DAD has dual functions in autoinhibition and nucleation; (2) the FH1, FH2, and DAD form a tripartite nucleation machine; and (3) formins nucleate by recruiting actin monomers and therefore are more similar to other nucleators than previously thought.
authors.affiliation: Department of Biology, Brandeis University, Waltham, MA 02454, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Gould
authors.forename: Sankar
authors.initials: S
authors.lastname: Maiti
authors.forename: Alphée
authors.initials: A
authors.lastname: Michelot
authors.forename: Brian R
authors.initials: BR
authors.lastname: Graziano
authors.forename: Laurent
authors.initials: L
authors.lastname: Blanchoin
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Goode
mesh_terms: D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D003001:Cloning, Molecular; D004926:Escherichia coli; D000080865:Formins; D006801:Humans; D016297:Mutagenesis, Site-Directed; D051304:Profilins / Q000378:metabolism*; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary / Q000502:physiology*; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D017422:Sequence Analysis, DNA; D059008:Time-Lapse Imaging
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; C108962:DIAPH1 protein, human; D000080865:Formins; D051304:Profilins; D011993:Recombinant Fusion Proteins