Mechanistic Differences in Actin Bundling Activity of Two Mammalian Formins, FRL1 and mDia2

Formin proteins are regulators of actin dynamics, mediating assembly of unbranched actin filaments. These multidomain proteins are defined by the presence of a Formin Homology 2 (FH2) domain. Previous work has shown that FH2 domains bind to filament barbed ends and move processively at the barbed end as the filament elongates. Here we report that two FH2 domains, from mammalian FRL1 and mDia2, also bundle filaments, whereas the FH2 domain from mDia1 cannot under similar conditions. The FH2 domain alone is sufficient for bundling. Bundled filaments made by either FRL1 or mDia2 are in both parallel and anti-parallel orientations. A novel property that might contribute to bundling is the ability of the dimeric FH2 domains from both FRL1 and mDia2 to dissociate and recombine. This property is not observed for mDia1. A difference between FRL1 and mDia2 is that FRL1-mediated bundling is competitive with barbed end binding, whereas mDia2-mediated bundling is not. Mutation of a highly conserved isoleucine residue in the FH2 domain does not inhibit bundling by either FRL1 or mDia2, but inhibits barbed end activities. However, the severity of this mutation varies between formins. For mDia1 and mDia2, the mutation strongly inhibits all effects of barbed end binding, but affects FRL1 much less strongly. Furthermore, our results suggest that the Ile mutation affects processivity. Taken together, our data suggest that the bundling activities of FRL1 and mDia2, while producing phenotypically similar bundles, differ in mechanistic detail. Formin proteins are regulators of actin dynamics, mediating assembly of unbranched actin filaments. These multidomain proteins are defined by the presence of a Formin Homology 2 (FH2) domain. Previous work has shown that FH2 domains bind to filament barbed ends and move processively at the barbed end as the filament elongates. Here we report that two FH2 domains, from mammalian FRL1 and mDia2, also bundle filaments, whereas the FH2 domain from mDia1 cannot under similar conditions. The FH2 domain alone is sufficient for bundling. Bundled filaments made by either FRL1 or mDia2 are in both parallel and anti-parallel orientations. A novel property that might contribute to bundling is the ability of the dimeric FH2 domains from both FRL1 and mDia2 to dissociate and recombine. This property is not observed for mDia1. A difference between FRL1 and mDia2 is that FRL1-mediated bundling is competitive with barbed end binding, whereas mDia2-mediated bundling is not. Mutation of a highly conserved isoleucine residue in the FH2 domain does not inhibit bundling by either FRL1 or mDia2, but inhibits barbed end activities. However, the severity of this mutation varies between formins. For mDia1 and mDia2, the mutation strongly inhibits all effects of barbed end binding, but affects FRL1 much less strongly. Furthermore, our results suggest that the Ile mutation affects processivity. Taken together, our data suggest that the bundling activities of FRL1 and mDia2, while producing phenotypically similar bundles, differ in mechanistic detail. Formin proteins have emerged as important actin filament assembly factors. Mammals have 15 formin isoforms, which segregate into seven distinct groups based on Formin Homology 2 (FH2) 3The abbreviations used are: FH2, formin homology domain 2; FRL, formin-related gene in leukocytes; mDia, mammalian diaphanous formin; DTT, dithiothreitol; GST, glutathione S-transferase; Arp2/3, actin-related protein 2/3; MALDI, matrix-assisted laser desorption/ionization-time of flight; TRITC, tetramethylrhodamine isothiocyanate; FITC, fluorescein isothiocyanate; au, arbitrary unit; NTA, nitrilotriacetic acid. 3The abbreviations used are: FH2, formin homology domain 2; FRL, formin-related gene in leukocytes; mDia, mammalian diaphanous formin; DTT, dithiothreitol; GST, glutathione S-transferase; Arp2/3, actin-related protein 2/3; MALDI, matrix-assisted laser desorption/ionization-time of flight; TRITC, tetramethylrhodamine isothiocyanate; FITC, fluorescein isothiocyanate; au, arbitrary unit; NTA, nitrilotriacetic acid. domain phylogeny (1Higgs H.N. Peterson K.J. Mol. Biol. Cell. 2005; 16: 1-13Crossref PubMed Scopus (199) Google Scholar). The FH2 domain is the defining structural feature of this family, and is responsible for most formin effects on actin. A key functional feature is that the FH2 domain is dimeric (2Li F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar, 4Moseley J.B. Sagot I. Manning A.L. Xu Y. Eck M.J. Pellman D. Goode B.L. Mol. Biol. Cell. 2004; 15: 896-907Crossref PubMed Scopus (221) Google Scholar, 5Xu Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). on the FH2 domain from that this has ability to dissociate Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). For all to the FH2 domain to the actin filament barbed and processively as the barbed end elongates. This ability to of and of barbed ends from protein in H.N. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). to barbed end binding, also bind actin filament E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google and bundle filaments Cell. 2005; PubMed Scopus Google Scholar, J.B. Goode B.L. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). structural have our of with filament barbed The of the FH2 domain to a anti-parallel with a by two of between Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). that on the of the are for actin assembly and from This is but of between the Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). A of the FH2 domain in with actin this the presence of actin on the of the 2005; 13: Scholar). a has a two for FH2 domain at the barbed end 2005; 13: Scholar). actin is The of FH2 domains are much less two have shown to bind to filament mammalian FRL1 E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google and Cell. 2005; PubMed Scopus Google Scholar). A has shown to bundle filaments, that also bind filament J.B. Goode B.L. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). is not a property conserved all formins. For FH2 of mDia1 bind filaments (2Li F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar). The functional of formin are not For both and to filament bundling Cell. 2005; PubMed Scopus Google Scholar, J.B. Goode B.L. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). filament by results in of filaments into is on bundling is For the domain is in to the FH2 domain for that the FH2 are for Cell. 2005; PubMed Scopus Google Scholar). The bundling for a and FH2 domains, in to to the FH2 J.B. Goode B.L. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). is not the FH2 domain is sufficient for bundling activities. this we the of mammalian FRL1 and the mDia1 and mDia2 that dimeric FH2 of mDia2, FRL1 but in to bind to filament FRL1 and mDia2 also filaments into bundles, whereas mDia1 does not. and the FH2 domain alone sufficient for bundling and actin filaments in bundling by FRL1 or to filament binding, FRL1 and mDia2 two that FH2 and FH2 the by which FRL1 and mDia2 bind to and bundle filaments by FRL1 is competitive with barbed end binding, while mDia2 bundling is not. suggest that FRL1 from mDia1 and mDia2 in with barbed ends as of mDia1 and FRL1 this is the by and into as (2Li F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar). The mDia2 used as a a from from by to the of the formin in used 2 DTT, and as but with of and as but with of either or with used for as the and FH2 of mDia2, and FRL1 as glutathione proteins in as (2Li F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar, F. Higgs H.N. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). from and all proteins as a on with to of in and with and at to and the at or on in DTT, and and by which with but with to a of to and the for or protein from the with and with and for 15 which to by as FRL1 at and with a from a from that from the at this The by matrix-assisted laser and FRL1 in 2 and not FRL1 activities mDia1 and mDia2 by from and in 2 and at formin in the as FRL1 with as FRL1 for 2 in and with a of for at to the and on a The in the domain and in the FH2 domain. by we not which actin from J. Biol. Chem. Full Text PDF PubMed Google and with J. PubMed Scopus Google Scholar). and actin on Cell. Full Text PDF PubMed Scopus Google and in at actin from in and by a of and by on in a from of protein a from and of a and For in at at and by at and by and from For of in the as for at and for and 15 at at and by used to and used to the used to at for and and to a in of is for 2 at in by of This actin to in in the or presence of in to a of to at at for at in a of and in of of the with of in of and by For in the presence of actin filaments at for at in a and and with to for at and at for at in a and and with This actin to in in the or presence of formin and as as for with the in and in a at for at For 2 actin with FRL1 or mDia2 in and at for and For actin filaments by a filaments with either FRL1 or mDia2 for or with protein for by of FRL1 or and as for at at in with from this into and for at of formin or to filaments and by and with of DTT, to with on and with a to for filaments or filament bundles, on the to filament bundles, bundling as with the that actin filaments with of filaments in bundles, we used a 2 actin with in for a of and to at for and in a at for at to from filaments. The and the into of actin and at for to filament by with as of actin and mDia2 in the and in the by the of actin filaments in bundles, 2 actin with FRL1 or mDia2 in with to and with at for to and with a with a filament at by and actin in to actin of the actin This to by 2 of at in to by of to a of with the made by proteins for to to actin to the in a The between of and of data for and between and 15 of from at the of to filament under the of to barbed ends with a of J. 2005; Full Text Full Text PDF PubMed Scopus Google to the is filament in is to and is at is by the is in arbitrary is of and and are of and actin in actin at to in the presence of and at for in a The to in with by two a of this into and to at formin protein to filaments, by and at for 2 2 at of 2 to the filaments with a by and two and into the for by the of in the actin and For protein with mDia1 and mDia2, protein and formin to filaments, and for 2 of For with formin with filaments for by with protein for of FH2 FRL1 or a of both in 2 DTT, and of and at for of to of with the and at with for at at and two with the and by results with The presence of the does not the of FRL1 in not between and and between and similar to the with the in 2 DTT, with for at with we with and which the results as two used not FRL1 and mDia2 whereas mDia1 that FH2 domain of FRL1 to filament whereas a similar mDia1 does not (2Li F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google that is not a feature of FH2 FH2 of mDia2 also bind to filaments with similar to that FRL1 and mDia2 FH2 domains might filaments into both bind with to filament and are this in which filament or whereas filaments in the and actin to at in a with at a of A mDia2 the and similar results not FRL1 and mDia2 and actin has on FRL1 or mDia2 filament or data not does not filaments at A mDia1 the FH2 and the also does not filaments not These data suggest that FRL1 and mDia2 filaments into whereas mDia1 does not. that FRL1 and mDia2 filament but not the of as in which filaments are and as in which filaments are not parallel to proteins as and filaments into under J. Full Text PDF PubMed Scopus Google Scholar, Y. D. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google whereas proteins as or bundle filaments at most with actin F. J. Biol. PubMed Scopus Google Scholar, Y. D. J. Mol. Biol. PubMed Scopus Google Scholar). the of and filament we used both and For we filaments the presence of either FRL1 or mDia2, a of filaments is into not filaments under conditions. with mDia1 have similar as actin filaments alone actin are by both FRL1 and mDia2 not The FH2 domain alone is sufficient for bundling by both FRL1 and mDia2 filaments are under bundling in both and in at the of FRL1 and mDia2 of the actin in the is at FRL1 and mDia2 in the This of formin and filaments at not that filaments are in between and filaments. FRL1 is into bundles, we FRL1 with is into and is not to FRL1 not and the bundle that FRL1 to bundling. not for mDia2, all not on and mDia2-mediated bundling and the of from to both and mDia2-mediated bundling and binding, but to at and in the presence of but strongly at A and much to and by and These results that with actin contribute to bundling for both but that FRL1 is less to in FRL1 and mDia2 of in in in which all barbed ends are the in which barbed and ends or in which filaments are parallel and are as and of in which the filaments in a parallel PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google Scholar, J. Biol. PubMed Scopus Google Scholar). filaments are in bundles, which the of J. Biol. PubMed Scopus Google and actin of but filaments I. PubMed Scopus Google Scholar). the of filaments in by FRL1 and mDia2, we FRL1 and mDia2 not with for filament binding, both formin and with actin in and data not shown for by either or filaments are in a with of both parallel and anti-parallel filaments and A that filaments are not parallel this are of actin and by of are by in the presence of actin actin and and to for this to end D. Cell. Full Text PDF PubMed Scopus Google Scholar, PubMed Scopus Google Scholar, PubMed Scopus Google Scholar, E.S. Higgs H.N. Cell. Full Text Full Text PDF PubMed Scopus Google filaments at the barbed from both ends of mDia2 in this that barbed ends are in both and data Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google the FH2 domain of is a with for This a with for effects on actin the of the Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, 2005; 13: Scholar). The of of between (1Higgs H.N. Peterson K.J. Mol. Biol. Cell. 2005; 16: 1-13Crossref PubMed Scopus (199) Google Scholar, 5Xu Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google that FH2 domains bind barbed ends by similar filament is a to filament we to might with filament that FH2 domains with for filament as of FRL1 and mDia2, might with filaments by of two between the of the FH2 and the filament by distinct from used for barbed end or between the and the by similar as used for barbed end the FH2 that the FH2 domain to the barbed the filament this we FH2 domains and to with bind to whereas not is with to the of in the used two to by However, we similar results with and not to mDia2 of FRL1 to a similar as mDia2 we in with or in a of of and the we of This is dimeric at all to and a of and a of A and a dimeric have that and are dimeric at the used in this E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar, F. Higgs H.N. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). FRL1 by whereas mDia2 ability of FRL1 and mDia2 FH2 to dissociate that might bind actin filament by this a similar might for both barbed end and binding, and the two might under to the of FRL1 or mDia2 with the barbed end affects bundling 2 actin are with either or formin filament and at the filament barbed of is by whereas of is to the between barbed end and we in which we the of barbed ends by filaments to with filaments with either formin or with protein of with formin the FH2 domain bind both filament barbed ends and filament with the FH2 domain filament protein barbed end F. J. Curr. Biol. 2003; 13: Full Text Full Text PDF PubMed Scopus Google Scholar, Mol. Biol. Cell. 2005; 16: PubMed Scopus Google Scholar). is with filaments in the of the ability of to actin is with with protein A and mDia2 in the or presence of with a in bundling observed the of barbed ends is and These data suggest that barbed end by FRL1 ability to bundle filaments A and whereas mDia2 with the barbed end does not bundling ability and does not the of actin in FRL1 and mDia2 and filaments protein is mDia2 and FRL1 the of barbed end on we that we in barbed end Previous have shown that mutation of a conserved isoleucine residue in both Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google and a mDia1 D. Mol. Cell. 2004; 13: Full Text Full Text PDF PubMed Scopus Google FH2 domain effects on actin under the This residue the of the FH2 Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google and with actin 2005; 13: Scholar). made the in and for effects on actin to to results barbed end barbed end as by of with actin alone The for this is mDia2 does not inhibit barbed end at also our FRL1 for we that by E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar). However, we a in FRL1 to a similar as the mDia1 not in the barbed end mDia1 does not to barbed ends E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar). also all for the ability to barbed ends from for in the presence of protein whereas all have a ability to barbed ends that FRL1 filament but much of ability to with that this mutation the of FRL1 from the barbed this we in which filaments in the presence of FRL1 for the FRL1 protein by for the of protein in FRL1 These data suggest FRL1 is from the barbed end the protein to we the effects of on into the barbed end for and while Ile are and less and observed E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google FRL1 is a less which we at and less the mDia2 and mDia1 The Ile mutation affects FRL1 with a and the conserved Ile residue is for both mDia1 and mDia2 effects on actin but less important for that FRL1 that for Ile The Ile of both mDia2 and FRL1 bundle actin filaments, as observed by and A and in FRL1 is at bundling filaments to of the of mDia2 with actin results to the not the mDia2 ability to bundle is not competitive with ability to with barbed also in in which we the of filament barbed ends by as for to bundling is by FRL1 is to barbed ends inhibit bundling by FRL1 less by the this we the bundling of two mammalian FRL1 and These also filament binding, with our that formin to bundling. The FH2 domain is sufficient for both activities. similar of mDia1 not bind filaments (2Li F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google and not bundle under the conditions. in by both FRL1 and mDia2 filaments in both parallel and anti-parallel orientations. property that to bundling is the ability of FH2 for both FRL1 and mDia2 to dissociate and recombine. The FH2 of mDia1 is much However, FRL1 and mDia2 differ in that barbed end and bundling are competitive for whereas are not competitive for mutation of a Ile residue that barbed end does not bundling by mDia2 and FRL1 a under barbed ends are is and mDia2-mediated bundling are similar This is the to the bundling of in detail. our results of but also mechanistic and effects of FH2 of FH2 domains that are important to our of in of between FRL1 and feature between FRL1 and mDia2 is that both to bundle as to filaments into are observed at of either or this most bundling proteins as and F. J. Biol. PubMed Scopus Google Scholar, Y. D. J. Mol. Biol. PubMed Scopus Google as to which filaments at and at J. Full Text PDF PubMed Scopus Google Scholar, J. Full Text PDF PubMed Scopus Google Scholar). The feature between FRL1 and mDia2 is that both FH2 domain are of and mDia1 Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google FH2 This property is of for filament by both FRL1 and mDia2 bind filaments while mDia1 does not (2Li F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar, J.B. Goode B.L. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). of the FH2 in and a might the FH2 domain to bind filament by a similar to barbed end structural and that responsible for barbed end are on the of the FH2 Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, 2005; 13: Scholar). to for binding, the that FH2 a filament is this mDia1 bind filaments FH2 not dissociate is a for that are The feature between FRL1 and mDia2 is that both FH2 domains the FH2 domain of mDia1 a of the mDia2 FH2 domain on the of the mDia1 FH2 domain D. Mol. Cell. 2004; 13: Full Text Full Text PDF PubMed Scopus Google on the of mDia2 that are not for mDia1 to structural of FRL1 FH2 domain based on the mDia1 but with mDia2 that FRL1 also These bundling with the filament The that and FRL1-mediated bundling is to that between FH2 domains and actin are important for bundling. is that FH2 domains with bundle filaments, while with not. with this has a FH2 domain and does while has a FH2 domain and does not bundle and J.B. Goode B.L. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google of formin FH2 domains are to in a between of FRL1 and the are similar for both FRL1 and mDia2, our important The FRL1 bundling to with barbed end whereas mDia2 bundling is not. This difference is by distinct all of which that barbed end FRL1 bundling but not mDia2 bundling the Ile which barbed end by both mDia2 and has on mDia2-mediated bundling and the ability of FRL1 to bundle under barbed ends are of results is that barbed end with bundling for to of for barbed end might by a distinct of but might the FRL1 FH2 domain in a that bundling. either this is a difference between the bundling activities of FRL1 and mDia2, and mechanistic of our data not to as to bundling we two by which FH2 domains might is a for we this The ability of both FRL1 and mDia2 FH2 to dissociate the that might as a the of the as that barbed end the mDia1 FH2 does not does not bind filament and is to barbed end The that is with barbed end for mDia2 is not competitive with barbed end binding, For mDia2 FH2 domain might on to with the of the actin filament by of this by the FH2 have to for bundling by the but in to the for in end of formin to unbranched filaments, as to the by in Higgs H.N. E.S. Curr. Biol. 2005; 15: Full Text Full Text PDF PubMed Scopus Google Scholar). a of unbranched filament with a feature that of filaments. have in assembly of of might by mDia2 J. Curr. Biol. 2003; 13: Full Text Full Text PDF PubMed Scopus Google Scholar, Curr. Biol. 2005; 15: Full Text Full Text PDF PubMed Scopus Google and mDia2 to in Curr. Biol. 2005; 15: Full Text Full Text PDF PubMed Scopus Google Scholar). The formin from also assembly J. Biol. 2005; PubMed Scopus Google Scholar, J. 2005; PubMed Scopus Google Scholar). The which we to bundle based on actin J. 2005; PubMed Scopus Google Scholar, J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, J. 2003; PubMed Scopus Google Scholar). The Ile Mutation on and and structural have the of a Ile residue for FH2 domain effects at the barbed This residue is on the of the FH2 Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google and with actin in 2005; 13: Scholar). Mutation of this residue in both FH2 Y. J. Sagot I. F. Pellman D. Goode B.L. Eck M.J. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google and a mDia1 FH2 D. Mol. Cell. 2004; 13: Full Text Full Text PDF PubMed Scopus Google FH2 The effects of this mutation for mDia2 are much for mDia2 is strongly in all barbed end activities. The mDia1 is mDia2 to Taken with the of the barbed end and bundling activities for mDia2, the mutation results bundling For the mutation has effects on barbed end on and less while effects on protein strongly. of the effects of this we cannot on the of the barbed end and bundling for However, the that FRL1 bundling is less the by barbed ends that might to FRL1 bundling. made the effects of on barbed end both of which of FH2 domain the difference between FRL1 and in barbed end have shown that FRL1 is with mDia1 and mDia2, both are and a not observed for mDia1 or mDia2 F. Higgs H.N. Curr. Biol. 2003; 13: 1335-1340Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 3Harris E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar, and this FRL1 E.S. Li F. Higgs H.N. J. Biol. Chem. 2004; 279: 20076-20087Abstract Full Text Full Text PDF PubMed Scopus (163) Google might for a of ability to The is the in which the Ile mutation affects protein of all with protein at that barbed end However, the of formin from the barbed end in the is that the FH2 domain has ability to move processively with the barbed the Ile residue is for of the two for FH2 domain at the barbed end 2005; 13: Scholar). between two might for the Ile the barbed end the is that the formin is in effects on actin. to actin. the of varies from formin to that of FH2 are and that to FH2 to for actin and and of for for mDia2 of for and the at for for with and by of for D. with