Microscopic Evidence That Actin-interacting Protein 1 Actively Disassembles Actin-depolymerizing Factor/Cofilin-bound Actin Filaments

Abstract

Actin-depolymerizing factor (ADF)/cofilin and gelsolin are the two major factors to enhance actin filament disassembly. Actin-interacting protein 1 (AIP1) enhances fragmentation of ADF/cofilin-bound filaments and caps the barbed ends. However, the mechanism by which AIP1 disassembles ADF/cofilin-bound filaments is not clearly understood. Here, we directly observed the effects of these proteins on filamentous actin by fluorescence microscopy and gained novel insight into the function of ADF/cofilin and AIP1. ADF/cofilin severed filaments and AIP1 strongly enhanced disassembly at nanomolar concentrations. However, gelsolin, gelsolin-actin complex, or cytochalasin D did not enhance disassembly by ADF/cofilin, suggesting that the strong activity of AIP1 cannot be explained by simple barbed end capping. Barbed end capping by ADF/cofilin and AIP1 was weak and allowed filament elongation, whereas gelsolin or gelsolin-actin complex strongly capped and inhibited elongation. These results suggest that AIP has an active role in filament severing or depolymerization and that ADF/cofilin and AIP1 are distinct from gelsolin in modulating filament elongation. Actin-depolymerizing factor (ADF)/cofilin and gelsolin are the two major factors to enhance actin filament disassembly. Actin-interacting protein 1 (AIP1) enhances fragmentation of ADF/cofilin-bound filaments and caps the barbed ends. However, the mechanism by which AIP1 disassembles ADF/cofilin-bound filaments is not clearly understood. Here, we directly observed the effects of these proteins on filamentous actin by fluorescence microscopy and gained novel insight into the function of ADF/cofilin and AIP1. ADF/cofilin severed filaments and AIP1 strongly enhanced disassembly at nanomolar concentrations. However, gelsolin, gelsolin-actin complex, or cytochalasin D did not enhance disassembly by ADF/cofilin, suggesting that the strong activity of AIP1 cannot be explained by simple barbed end capping. Barbed end capping by ADF/cofilin and AIP1 was weak and allowed filament elongation, whereas gelsolin or gelsolin-actin complex strongly capped and inhibited elongation. These results suggest that AIP has an active role in filament severing or depolymerization and that ADF/cofilin and AIP1 are distinct from gelsolin in modulating filament elongation. The rearrangement of the actin cytoskeleton is controlled by dynamic assembly and disassembly of actin filaments. Regulated disassembly as well as assembly is important for maintaining constant turnover of actin filaments. Actin-depolymerizing factor (ADF) 1The abbreviations used are: ADF, actin-depolymerizing factor; AIP1, actin-interacting protein 1; GA, gelsolin-actin complex. 1The abbreviations used are: ADF, actin-depolymerizing factor; AIP1, actin-interacting protein 1; GA, gelsolin-actin complex./cofilin and gelsolin are the two major classes of actin-regulatory proteins that accelerate filament disassembly (1Southwick F.S. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 6936-6938Google Scholar). ADF/cofilin weakly severs filaments without capping ends and also enhances monomer dissociation from the ends in A. S. Scholar). gelsolin strongly severs filaments and caps the barbed ends in in and Scholar). actin-interacting protein 1 (AIP1) has to ADF/cofilin-bound filaments in S. Scholar). AIP1 caps the barbed ends of ADF/cofilin-bound filaments Scholar). capping activity is to to enhanced fragmentation by of filaments capping and fragmentation has not the of ADF/cofilin and AIP1 strong severing and capping of which are to the effects of However, of effects has not of actin-regulatory proteins by of However, the results of these are to or ADF/cofilin is for of ADF/cofilin to of the filaments and the fluorescence of that is to of actin S. which are used to the of and of the effects of proteins on actin filaments has used to filament severing by gelsolin or ADF/cofilin 2000; filament by Proc. Natl. Acad. Sci. U. S. A. 2000; S. and of filament by Scholar). has to the of Here, we used the to the mechanism of actin filament disassembly by ADF/cofilin and AIP1 in to the function of results suggest that AIP1 has an active role in filament disassembly and that ADF/cofilin and AIP1 distinct from and actin was as Scholar). S. and S. Sci. as was from as S. Scholar). complex was by and gelsolin in for at and to in an that D was from of and of actin filament severing by fluorescence microscopy was as 2000; of the we did not the of ADF/cofilin to actin S. Proc. Natl. Acad. Sci. U. S. A. Scholar). actin actin and actin at for in 1 1 and in and allowed to was on the two of to was to and into the to the actin was and into the and for The was and the of The proteins in and into the gelsolin, of was used to the observed by of and the by and by and or of the was end capping was by the of the actin filaments to actin filaments gelsolin, cytochalasin or gelsolin-actin complex in as for The was in and for actin was cytochalasin of cytochalasin D of from the barbed ends and the filaments for Barbed to actin from filament ends was as S. the that actin was used as in of and actin filament disassembly and severing by ADF/cofilin and AIP1, we used the by 2000; Scholar). filaments and and to that by The of the filaments was observed by fluorescence microscopy and or of the without the actin filaments for and The of the filaments was not from that ADF/cofilin S. filament severing and and the to was in the of filaments suggesting that filaments to or and AIP1 protein S. the of filaments and and filaments suggesting that filaments or the The of the filaments was However, did not of the filaments and or the of the filaments severing at at severing and disassembly at was at and at did not enhance disassembly D and in the of enhanced disassembly by was not and did not enhance disassembly and These results suggest that is strong disassembly factor and in to effects of and on actin filament severing and disassembly. actin filaments and or of or and as in the The filaments observed and and the and by fluorescence and the are for that AIP1 caps the barbed ends of ADF/cofilin-bound filaments and that capping activity of AIP1 enhances fragmentation by of filaments. However, results in that was to enhance disassembly of filaments of filaments was not to barbed end capping is for disassembly of barbed enhance disassembly in the of ADF/cofilin and the of AIP1 in the we the effects of gelsolin, and cytochalasin barbed on severing by and severed filaments and the to and the of gelsolin did not enhance disassembly and and the of the filaments was to that the and was in the of filaments the gelsolin and as be explained that barbed end capping by gelsolin from the barbed ends depolymerization is filament and disassembly. did not disassembly by and and and the of the filaments suggesting that the disassembly was not the of depolymerization from the barbed ends. filaments not by and and the of the filaments was to that by the gelsolin and filament severing and disassembly by and in the of gelsolin-actin complex or cytochalasin actin filaments and complex and and and and and and and and cytochalasin D and and and and and or and and The filaments observed and and the and by fluorescence and the are for has strong filament severing which to that gelsolin as barbed as in we the effects of gelsolin-actin on actin filament severing and disassembly by and The gelsolin-actin complex barbed ends and caps the barbed ends without severing the filaments. did not the of the filaments and did not enhance disassembly in the of and and suggesting that barbed end capping not enhance fragmentation by to gelsolin, did not disassembly by and and and did not filaments in the of and results by barbed cytochalasin D did not the of actin filaments and and did not enhance disassembly in the of and D did not disassembly by and and and did not filaments in the of cytochalasin D and These results capping strongly suggest that barbed end capping not enhance filament disassembly and that AIP1 an active role in severing or depolymerization of ADF/cofilin-bound by for by the ADF/cofilin and AIP1, we of protein and the effects on actin filaments. actin filaments for and by the enhanced disassembly whereas the did not disassembly did not filaments that the These results suggest that is to the filaments and disassembly by actin filaments severed the filaments the was from the filaments that and these results suggest that the of to actin filaments is for disassembly by of to actin for disassembly by actin filaments in The filaments and or for and and or for The and the and and the and and the are for or of Barbed by AIP1, and severs filaments and caps the barbed whereas ADF/cofilin severs filaments without capping ends. that AIP1 barbed end of ADF/cofilin-bound that AIP1 caps the barbed ends. the of ADF/cofilin and AIP1 the of the of actin S. Sci. Scholar). the actin that was used to the capping activity of AIP1 we that inhibited actin in the of that and the barbed end in to AIP1 and ADF/cofilin, depolymerization of of the filaments in the of AIP1 and the of barbed end by and was of in the or of and used as at to of as the of the in the The are as to that of as well as the of capping by gelsolin is from that by ADF/cofilin and AIP1, we directly observed the effects of these proteins on barbed end actin filaments gelsolin, or and was at which is the barbed end the end is to from the barbed ends. of filaments that at end and ends of filaments of and the of the filaments filaments that of was of filaments to and that gelsolin capped barbed ends and elongation. filaments suggesting that ends not filaments from end and in is for filament disassembly in the of capping by is and is to elongation. However, the filaments D and suggesting that capping by and is weak and not major of disassembly. of the filaments by suggesting that filaments The did not the of the filaments to and D and or gelsolin-actin complex and strongly inhibited of that the on barbed ends. these results suggest that gelsolin is distinct from ADF/cofilin and AIP1 in the of barbed end of actin from filament ends. actin filaments to and gelsolin and cytochalasin D or gelsolin-actin complex for and observed fluorescence of from is inhibited by gelsolin cytochalasin or gelsolin-actin complex not by or these filaments into filaments without filaments at the ends and filaments and the are of filaments are on the of the we that (AIP1) has strong activity to actin filaments in the of However, barbed end capping by gelsolin or cytochalasin D not the of AIP1 in the of that the by that AIP1 enhances fragmentation by capping ends of filaments and is not of the of AIP1. that AIP1 not enhance severing or end depolymerization by ADF/cofilin by However, in of ADF/cofilin was used at in whereas AIP1 was active ADF/cofilin was at actin S. Sci. Sci. Scholar). is that the of ADF/cofilin to results suggest that AIP1 has an active role in severing or depolymerization of ADF/cofilin-bound filaments. by microscopy and that the of actin filaments to S. A. 2000; Scholar). However, AIP1 the to in the of ADF/cofilin Sci. and actin in S. Sci. Sci. S. Scholar). results by are these also that of AIP1 is for suggesting that AIP1 disassembles filaments in to actin or that the function of AIP1 is to ADF/cofilin-bound filaments and into filaments. are not to AIP1 disassembles filaments by severing or of is that the depolymerization from ends the in the are to be the to depolymerization from the barbed ends by in the was not not filament disassembly by ADF/cofilin and AIP1 was and to the by to of actin at fluorescence microscopy be Proc. Natl. Acad. Sci. U. S. A. Scholar). also that capping by ADF/cofilin and AIP1 is weak and in to capping by that ADF/cofilin and AIP1 not function as an of actin are proteins to in of in S. Scholar). is in of and actin to the S. Sci. Scholar). However, the of is observed the of the filaments not to the the barbed ends are S. Sci. Scholar). also that barbed end capping is not major function of in the role of enhances fragmentation of actin filaments by severing or depolymerization and the in the actin in S. be to of we that AIP1 is factor to ADF/cofilin-bound actin filaments. The rearrangement of the actin cytoskeleton is controlled by dynamic assembly and disassembly of actin filaments. Regulated disassembly as well as assembly is important for maintaining constant turnover of actin filaments. Actin-depolymerizing factor (ADF) 1The abbreviations used are: ADF, actin-depolymerizing factor; AIP1, actin-interacting protein 1; GA, gelsolin-actin complex. 1The abbreviations used are: ADF, actin-depolymerizing factor; AIP1, actin-interacting protein 1; GA, gelsolin-actin complex./cofilin and gelsolin are the two major classes of actin-regulatory proteins that accelerate filament disassembly (1Southwick F.S. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 6936-6938Google Scholar). ADF/cofilin weakly severs filaments without capping ends and also enhances monomer dissociation from the ends in A. S. Scholar). gelsolin strongly severs filaments and caps the barbed ends in in and Scholar). actin-interacting protein 1 (AIP1) has to ADF/cofilin-bound filaments in S. Scholar). AIP1 caps the barbed ends of ADF/cofilin-bound filaments Scholar). capping activity is to to enhanced fragmentation by of filaments capping and fragmentation has not the of ADF/cofilin and AIP1 strong severing and capping of which are to the effects of However, of effects has not The of actin-regulatory proteins by of However, the results of these are to or ADF/cofilin is for of ADF/cofilin to of the filaments and the fluorescence of that is to of actin S. which are used to the of and of the effects of proteins on actin filaments has used to filament severing by gelsolin or ADF/cofilin 2000; filament by Proc. Natl. Acad. Sci. U. S. A. 2000; S. and of filament by Scholar). has to the of Here, we used the to the mechanism of actin filament disassembly by ADF/cofilin and AIP1 in to the function of results suggest that AIP1 has an active role in filament disassembly and that ADF/cofilin and AIP1 distinct from and actin was as Scholar). S. and S. Sci. as was from as S. Scholar). complex was by and gelsolin in for at and to in an that D was from of and of actin filament severing by fluorescence microscopy was as 2000; of the we did not the of ADF/cofilin to actin S. Proc. Natl. Acad. Sci. U. S. A. Scholar). actin actin and actin at for in 1 1 and in and allowed to was on the two of to was to and into the to the actin was and into the and for The was and the of The proteins in and into the gelsolin, of was used to the observed by of and the by and by and or of the was end capping was by the of the actin filaments to actin filaments gelsolin, cytochalasin or gelsolin-actin complex in as for The was in and for actin was cytochalasin of cytochalasin D of from the barbed ends and the filaments for Barbed to actin from filament ends was as S. the that actin was used as in and actin was as Scholar). S. and S. Sci. as was from as S. Scholar). complex was by and gelsolin in for at and to in an that D was from of and of actin filament severing by fluorescence microscopy was as 2000; of the we did not the of ADF/cofilin to actin S. Proc. Natl. Acad. Sci. U. S. A. Scholar). actin actin and actin at for in 1 1 and in and allowed to was on the two of to was to and into the to the actin was and into the and for The was and the of The proteins in and into the gelsolin, of was used to the observed by of and the by and by and or of the was Barbed end capping was by the of the actin filaments to actin filaments gelsolin, cytochalasin or gelsolin-actin complex in as for The was in and for actin was cytochalasin of cytochalasin D of from the barbed ends and the filaments for Barbed to actin from filament ends was as S. the that actin was used as in of and actin filament disassembly and severing by ADF/cofilin and AIP1, we used the by 2000; Scholar). filaments and and to that by The of the filaments was observed by fluorescence microscopy and or of the without the actin filaments for and The of the filaments was not from that ADF/cofilin S. filament severing and and the to was in the of filaments suggesting that filaments to or and AIP1 protein S. the of filaments and and filaments suggesting that filaments or the The of the filaments was However, did not of the filaments and or the of the filaments severing at at severing and disassembly at was at and at did not enhance disassembly D and in the of enhanced disassembly by was not and did not enhance disassembly and These results suggest that is strong disassembly factor and in to that AIP1 caps the barbed ends of ADF/cofilin-bound filaments and that capping activity of AIP1 enhances fragmentation by of filaments. However, results in that was to enhance disassembly of filaments of filaments was not to barbed end capping is for disassembly of barbed enhance disassembly in the of ADF/cofilin and the of AIP1 in the we the effects of gelsolin, and cytochalasin barbed on severing by and severed filaments and the to and the of gelsolin did not enhance disassembly and and the of the filaments was to that the and was in the of filaments the gelsolin and as be explained that barbed end capping by gelsolin from the barbed ends depolymerization is filament and disassembly. did not disassembly by and and and the of the filaments suggesting that the disassembly was not the of depolymerization from the barbed ends. filaments not by and and the of the filaments was to that by the gelsolin and filament severing and disassembly by and in the of gelsolin-actin complex or cytochalasin actin filaments and complex and and and and and and and and cytochalasin D and and and and and or and and The filaments observed and and the and by fluorescence and the are for has strong filament severing which to that gelsolin as barbed as in we the effects of gelsolin-actin on actin filament severing and disassembly by and The gelsolin-actin complex barbed ends and caps the barbed ends without severing the filaments. did not the of the filaments and did not enhance disassembly in the of and and suggesting that barbed end capping not enhance fragmentation by to gelsolin, did not disassembly by and and and did not filaments in the of and results by barbed cytochalasin D did not the of actin filaments and and did not enhance disassembly in the of and D did not disassembly by and and and did not filaments in the of cytochalasin D and These results capping strongly suggest that barbed end capping not enhance filament disassembly and that AIP1 an active role in severing or depolymerization of ADF/cofilin-bound by for by the ADF/cofilin and AIP1, we of protein and the effects on actin filaments. actin filaments for and by the enhanced disassembly whereas the did not disassembly did not filaments that the These results suggest that is to the filaments and disassembly by actin filaments severed the filaments the was from the filaments that and these results suggest that the of to actin filaments is for disassembly by of to actin for disassembly by actin filaments in The filaments and or for and and or for The and the and and the and and the are for or of Barbed by AIP1, and severs filaments and caps the barbed whereas ADF/cofilin severs filaments without capping ends. that AIP1 barbed end of ADF/cofilin-bound that AIP1 caps the barbed ends. the of ADF/cofilin and AIP1 the of the of actin S. Sci. Scholar). the actin that was used to the capping activity of AIP1 we that inhibited actin in the of that and the barbed end in to AIP1 and ADF/cofilin, depolymerization of of the filaments in the of AIP1 and the of barbed end by and was of in the or of and used as at to of as the of the in the The are as to that of as well as the of capping by gelsolin is from that by ADF/cofilin and AIP1, we directly observed the effects of these proteins on barbed end actin filaments gelsolin, or and was at which is the barbed end the end is to from the barbed ends. of filaments that at end and ends of filaments of and the of the filaments filaments that of was of filaments to and that gelsolin capped barbed ends and elongation. filaments suggesting that ends not filaments from end and in is for filament disassembly in the of capping by is and is to elongation. However, the filaments D and suggesting that capping by and is weak and not major of disassembly. of the filaments by suggesting that filaments The did not the of the filaments to and D and or gelsolin-actin complex and strongly inhibited of that the on barbed ends. these results suggest that gelsolin is distinct from ADF/cofilin and AIP1 in the of barbed end of actin from filament ends. actin filaments to and gelsolin and cytochalasin D or gelsolin-actin complex for and observed fluorescence of from is inhibited by gelsolin cytochalasin or gelsolin-actin complex not by or these filaments into filaments without filaments at the ends and filaments and the are of filaments are on the of the of and actin filament disassembly and severing by ADF/cofilin and AIP1, we used the by 2000; Scholar). filaments and and to that by The of the filaments was observed by fluorescence microscopy and or of the without the actin filaments for and The of the filaments was not from that ADF/cofilin S. filament severing and and the to was in the of filaments suggesting that filaments to or and AIP1 protein S. the of filaments and and filaments suggesting that filaments or the The of the filaments was However, did not of the filaments and or the of the filaments severing at at severing and disassembly at was at and at did not enhance disassembly D and in the of enhanced disassembly by was not and did not enhance disassembly and These results suggest that is strong disassembly factor and in to that AIP1 caps the barbed ends of ADF/cofilin-bound filaments and that capping activity of AIP1 enhances fragmentation by of filaments. However, results in that was to enhance disassembly of filaments of filaments was not to barbed end capping is for disassembly of barbed enhance disassembly in the of ADF/cofilin and the of AIP1 in the we the effects of gelsolin, and cytochalasin barbed on severing by and severed filaments and the to and the of gelsolin did not enhance disassembly and and the of the filaments was to that the and was in the of filaments the gelsolin and as be explained that barbed end capping by gelsolin from the barbed ends depolymerization is filament and disassembly. did not disassembly by and and and the of the filaments suggesting that the disassembly was not the of depolymerization from the barbed ends. filaments not by and and the of the filaments was to that by the gelsolin and has strong filament severing which to that gelsolin as barbed as in we the effects of gelsolin-actin on actin filament severing and disassembly by and The gelsolin-actin complex barbed ends and caps the barbed ends without severing the filaments. did not the of the filaments and did not enhance disassembly in the of and and suggesting that barbed end capping not enhance fragmentation by to gelsolin, did not disassembly by and and and did not filaments in the of and results by barbed cytochalasin D did not the of actin filaments and and did not enhance disassembly in the of and D did not disassembly by and and and did not filaments in the of cytochalasin D and These results capping strongly suggest that barbed end capping not enhance filament disassembly and that AIP1 an active role in severing or depolymerization of ADF/cofilin-bound filaments. by for by the ADF/cofilin and AIP1, we of protein and the effects on actin filaments. actin filaments for and by the enhanced disassembly whereas the did not disassembly did not filaments that the These results suggest that is to the filaments and disassembly by actin filaments severed the filaments the was from the filaments that and these results suggest that the of to actin filaments is for disassembly by of Barbed by AIP1, and severs filaments and caps the barbed whereas ADF/cofilin severs filaments without capping ends. that AIP1 barbed end of ADF/cofilin-bound that AIP1 caps the barbed ends. the of ADF/cofilin and AIP1 the of the of actin S. Sci. Scholar). the actin that was used to the capping activity of AIP1 we that inhibited actin in the of that and the barbed end in to AIP1 and ADF/cofilin, depolymerization of of the filaments in the of AIP1 and the capping by gelsolin is from that by ADF/cofilin and AIP1, we directly observed the effects of these proteins on barbed end actin filaments gelsolin, or and was at which is the barbed end the end is to from the barbed ends. of filaments that at end and ends of filaments of and the of the filaments filaments that of was of filaments to and that gelsolin capped barbed ends and elongation. filaments suggesting that ends not filaments from end and in is for filament disassembly in the of capping by is and is to elongation. However, the filaments D and suggesting that capping by and is weak and not major of disassembly. of the filaments by suggesting that filaments The did not the of the filaments to and D and or gelsolin-actin complex and strongly inhibited of that the on barbed ends. these results suggest that gelsolin is distinct from ADF/cofilin and AIP1 in the of barbed end elongation. we that (AIP1) has strong activity to actin filaments in the of However, barbed end capping by gelsolin or cytochalasin D not the of AIP1 in the of that the by that AIP1 enhances fragmentation by capping ends of filaments and is not of the of AIP1. that AIP1 not enhance severing or end depolymerization by ADF/cofilin by However, in of ADF/cofilin was used at in whereas AIP1 was active ADF/cofilin was at actin S. Sci. Sci. Scholar). is that the of ADF/cofilin to results suggest that AIP1 has an active role in severing or depolymerization of ADF/cofilin-bound filaments. by microscopy and that the of actin filaments to S. A. 2000; Scholar). However, AIP1 the to in the of ADF/cofilin Sci. and actin in S. Sci. Sci. S. Scholar). results by are these also that of AIP1 is for suggesting that AIP1 disassembles filaments in to actin or that the function of AIP1 is to ADF/cofilin-bound filaments and into filaments. are not to AIP1 disassembles filaments by severing or of is that the depolymerization from ends the in the are to be the to depolymerization from the barbed ends by in the was not not filament disassembly by ADF/cofilin and AIP1 was and to the by to of actin at fluorescence microscopy be Proc. Natl. Acad. Sci. U. S. A. Scholar). also that capping by ADF/cofilin and AIP1 is weak and in to capping by that ADF/cofilin and AIP1 not function as an of actin are proteins to in of in S. Scholar). is in of and actin to the S. Sci. Scholar). However, the of is observed the of the filaments not to the the barbed ends are S. Sci. Scholar). also that barbed end capping is not major function of in the role of enhances fragmentation of actin filaments by severing or depolymerization and the in the actin in S. be to of we that AIP1 is factor to ADF/cofilin-bound actin filaments. we that (AIP1) has strong activity to actin filaments in the of However, barbed end capping by gelsolin or cytochalasin D not the of AIP1 in the of that the by that AIP1 enhances fragmentation by capping ends of filaments and is not of the of AIP1. that AIP1 not enhance severing or end depolymerization by ADF/cofilin by However, in of ADF/cofilin was used at in whereas AIP1 was active ADF/cofilin was at actin S. Sci. Sci. Scholar). is that the of ADF/cofilin to AIP1. results suggest that AIP1 has an active role in severing or depolymerization of ADF/cofilin-bound filaments. by microscopy and that the of actin filaments to S. A. 2000; Scholar). However, AIP1 the to in the of ADF/cofilin Sci. and actin in S. Sci. Sci. S. Scholar). results by are these also that of AIP1 is for suggesting that AIP1 disassembles filaments in to actin or that the function of AIP1 is to ADF/cofilin-bound filaments and into filaments. are not to AIP1 disassembles filaments by severing or of is that the depolymerization from ends the in the are to be the to depolymerization from the barbed ends by in the was not not filament disassembly by ADF/cofilin and AIP1 was and to the by to of actin at fluorescence microscopy be Proc. Natl. Acad. Sci. U. S. A. Scholar). also that capping by ADF/cofilin and AIP1 is weak and in to capping by that ADF/cofilin and AIP1 not function as an of actin are AIP1 proteins to in of in S. Scholar). is in of and actin to the S. Sci. Scholar). However, the of is observed the of the filaments not to the the barbed ends are S. Sci. Scholar). also that barbed end capping is not major function of in the role of enhances fragmentation of actin filaments by severing or depolymerization and the in the actin in S. be to of we that AIP1 is factor to ADF/cofilin-bound actin filaments. A. for