Structure of the formin-interaction domain of the actin nucleation-promoting factor Bud6

Tu, Daqi; Graziano, Brian R.; Park, Eun‐Young; Zheng, Wei; Li, Yiqun; Goode, Bruce L.; Eck, Michael J.

doi:10.1073/pnas.1203035109

Cited by 32 publications

(57 citation statements)

References 65 publications

(81 reference statements)

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“…As outlined above, other formins are activated by actin-binding protein domains that act either externally (like Bud6, which activates Bni1 and also binds actin in a WH2-like fashion (35,37) or internally (like the C-terminal WH2 domain of INF2 or FMNL3 (30,31)). The model we present here for the role of FSI in the processive function of Fmn2 may thus have general significance regarding the regulation of other formins.…”

Section: Discussionmentioning

confidence: 99%

Role of the C-terminal Extension of Formin 2 in Its Activation by Spire Protein and Processive Assembly of Actin Filaments

Montaville¹,

Kühn²,

Compper

et al. 2016

Journal of Biological Chemistry

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Formin 2 (Fmn2), a member of the FMN family of formins, plays an important role in early development. This formin cooperates with profilin and Spire, a WASP homology domain 2 (WH2) repeat protein, to stimulate assembly of a dynamic cytoplasmic actin meshwork that facilitates translocation of the meiotic spindle in asymmetric division of mouse oocytes. The kinase-like non-catalytic domain (KIND) of Spire directly interacts with the C-terminal extension of the formin homology domain 2 (FH2) domain of Fmn2, called FSI. This direct interaction is required for the synergy between the two proteins in actin assembly. We have recently demonstrated how Spire, which caps barbed ends via its WH2 domains, activates Fmn2. Fmn2 by itself associates very poorly to filament barbed ends but is rapidly recruited to Spire-capped barbed ends via the KIND domain, and it subsequently displaces Spire from the barbed end to elicit rapid processive assembly from profilin⅐actin. Here, we address the mechanism by which Spire and Fmn2 compete at barbed ends and the role of FSI in orchestrating this competition as well as in the processivity of Fmn2. We have combined microcalorimetric, fluorescence, and hydrodynamic binding assays, as well as bulk solution and single filament measurements of actin assembly, to show that removal of FSI converts Fmn2 into a Capping Protein. This activity is mimicked by association of KIND to Fmn2. In addition, FSI binds actin at filament barbed ends as a weak capper and plays a role in displacing the WH2 domains of Spire from actin, thus allowing the association of actin-binding regions of FH2 to the barbed end.Polarized assembly of actin filaments is pivotal in motile processes. It is precisely regulated by proteins that bind the barbed ends of actin filaments and either block or assist filament assembly using various mechanisms (1). Among these regulators, formins are acknowledged to nucleate and track filament barbed ends, mediating rapid processive elongation of filaments (2, 3). In contrast, WASP homology 2 (WH2) 3 repeatcontaining proteins display versatile barbed end capping or tracking and filament severing activities (4). In early oogenesis of Drosophila as well as in mammalian meiosis, a formin (Fmn2/Cappuccino) and a WH2-repeat protein (Spire) synergize in an intriguing fashion to stimulate massive assembly of a dynamic cytoplasmic actin meshwork, required for completion of crucial steps in axis patterning or asymmetric division (5-12). This complexity adds to the known need of profilin for rapid processive assembly of all formins, including Cappuccino (9). Like most formins, Fmn2 harbors conserved C-terminal formin homology 1 (FH1) and formin homology 2 (FH2) domains. The C-terminal FH1-FH2 domain of Fmn2 represents a constitutive active module in which the FH1 domain binds profilin and the FH2 domain to the barbed end of F-actin. The head-to-tail FH2 dimer of formins is thought, from structural data, to encircle the terminal and subterminal actin subunits that constitute the barbed end of the fil...

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Section: Discussionmentioning

confidence: 99%

Role of the C-terminal Extension of Formin 2 in Its Activation by Spire Protein and Processive Assembly of Actin Filaments

Montaville¹,

Kühn²,

Compper

et al. 2016

Journal of Biological Chemistry

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“…Hence, nucleation of actin filaments in vitro does not appear to be a common property of formins. In fact, it is emerging that actin nucleation activity of formins may involve additional cellular co-factors: The yeast formin Bni1 interacts via the FH2 domain with the polarity factor Bud6 (Moseley and Goode, 2005;Tu et al, 2012), the drosophila formin Cappuccino and Spire cooperate for actin nucleation (Quinlan et al, 2007), and mDia1 synergizes with the APC (adenomatous polyposis coli) protein for actin nucleation Okada et al, 2010). Thus, we cannot rule out that FHOD1 may associate with an additional factor for actin nucleation in cells.…”

Section: Fhod1 Bundling In Actin Arcs 1897mentioning

confidence: 99%

FHOD1 is a combined actin filament capping and bundling factor that selectively associates with actin arcs and stress fibers

Schönichen

Mannherz

Behrmann

et al. 2013

Journal of Cell Science

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SummaryFormins are actin polymerization factors that are known to nucleate and elongate actin filaments at the barbed end. In the present study we show that human FHOD1 lacks actin nucleation and elongation capacity, but acts as an actin bundling factor with capping activity toward the filament barbed end. Constitutively active FHOD1 associates with actin filaments in filopodia and lamellipodia at the leading edge, where it moves with the actin retrograde flow. At the base of lamellipodia, FHOD1 is enriched in nascent, bundled actin arcs as well as in more mature stress fibers. This function requires actin-binding domains located N-terminally to the canonical FH1-FH2 element. The bundling phenotype is maintained in the presence of tropomyosin, confirmed by electron microscopy showing assembly of 5 to 10 actin filaments into parallel, closely spaced filament bundles. Taken together, our data suggest a model in which FHOD1 stabilizes actin filaments by protecting barbed ends from depolymerization with its dimeric FH2 domain, whereas the region N-terminal to the FH1 domain mediates F-actin bundling by simultaneously binding to the sides of adjacent F-actin filaments.

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“…However, NPFs effectively compete with profilin for actin monomer binding, and organize mutiple actin monomers in proximity to the formin FH2 domain. Such NPF-formin pairs include Bud6-Bni1, Spire-FMN (Spir and Cappuccino in Drosophila) and adenomateous polyposis coli protein (APC)-mDia1 Quinlan et al, 2007;Webb et al, 2009;Okada et al, 2010;Graziano et al, 2011;Tu et al, 2012). In vivo, Bni1-Bud6 and APC-mDia1 function together to assemble actin cables and pseudocleavage furrows, respectively, and have also been shown to directly interact in vitro to assemble actin in the presence of profilin and/or capping protein Okada et al, 2010;Graziano et al, 2011;Breitsprecher et al, 2012).…”

Section: Mechanism Of Actin Nucleationmentioning

confidence: 99%

Formins at a glance

Breitsprecher

Goode

2013

Journal of Cell Science

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242

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Structure of the formin-interaction domain of the actin nucleation-promoting factor Bud6

Cited by 32 publications

References 65 publications

Role of the C-terminal Extension of Formin 2 in Its Activation by Spire Protein and Processive Assembly of Actin Filaments

Role of the C-terminal Extension of Formin 2 in Its Activation by Spire Protein and Processive Assembly of Actin Filaments

FHOD1 is a combined actin filament capping and bundling factor that selectively associates with actin arcs and stress fibers

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