title: Competitive displacement of cofilin can promote actin filament severing.
abstract: Cofilin is an essential actin filament severing protein that functions in the dynamic remodeling of the actin cytoskeleton. Filament severing activity is most efficient at sub-stoichiometric cofilin binding densities (i.e. <1 cofilin per actin filament subunit), and peaks when the number density of boundaries (i.e. junctions) between bare and cofilin-decorated segments is maximal. A model in which local topological and mechanical discontinuities lead to preferential fragmentation at boundaries accounts for available experimental data, including direct visualization of cofilin and actin during real-time severing events. The boundary-severing model predicts that ligands (e.g. other actin-binding proteins) that compete with cofilin for actin filament binding and modulate cofilin occupancy on filaments will alter the bare-decorated segment boundary density, and thus, the filament severing activity of cofilin. Here, we directly test this model prediction by evaluating the effects of phalloidin and myosin, two ligands that compete with cofilin for filament binding, on the actin filament binding and severing activities of cofilin. Our experiments demonstrate that competitive displacement of cofilin lowers cofilin occupancy and promotes severing when initial cofilin occupancy is high (i.e. >50%). Even in the presence of competitive ligands, maximum severing activity occurs when cofilin-decorated boundary density is highest, consistent with preferential fragmentation at boundaries. We propose a general "severodyne" framework for the modulation of cofilin-mediated actin filament severing by small molecule or actin-binding protein ligands that compete with cofilin for actin filament binding.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
authors.forename: W Austin
authors.initials: WA
authors.lastname: Elam
authors.forename: Hyeran
authors.initials: H
authors.lastname: Kang
authors.forename: Enrique M
authors.initials: EM
authors.lastname: De La Cruz
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D000818:Animals; D051338:Cofilin 1 / Q000378:metabolism*; D006801:Humans; D009218:Myosins / Q000378:metabolism; D010590:Phalloidine / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D051338:Cofilin 1; D011994:Recombinant Proteins; D010590:Phalloidine; D009218:Myosins
keywords: Actin binding protein; Competition; Cytoskeleton; L(avg); Myosin; N-ethylmaleimide; NEM; Phalloidin; S1; XAip1; Xenopus Actin-interacting protein 1; average filament length; cofilin binding density; subfragment 1; ν(cof)
references.citation: Biochem J. 1988 Apr 1;251(1):121-7
references.pmid: 3390149
references.citation: Proc Natl Acad Sci U S A. 1987 Aug;84(15):5262-6
references.pmid: 3474653
references.citation: Biochemistry. 1967 Jul;6(7):1948-54
references.pmid: 6049437
references.citation: Nature. 1998 Jun 25;393(6687):805-9
references.pmid: 9655397
references.citation: Cell. 2003 Feb 21;112(4):453-65
references.pmid: 12600310
references.citation: J Biol Chem. 1991 Sep 15;266(26):17218-21
references.pmid: 1654325
references.citation: Curr Biol. 2011 May 24;21(10):862-8
references.pmid: 21530260
references.citation: Annu Rev Cell Dev Biol. 1999;15:185-230
references.pmid: 10611961
references.citation: Mol Cell. 2006 Oct 6;24(1):13-23
references.pmid: 17018289
references.citation: Trends Biochem Sci. 2000 Jan;25(1):19-23
references.pmid: 10637608
references.citation: J Mol Biol. 2000 May 12;298(4):649-61
references.pmid: 10788327
references.citation: J Mol Biol. 2002 Jan 25;315(4):911-25
references.pmid: 11812157
references.citation: Anat Sci Int. 2004 Dec;79(4):173-83
references.pmid: 15633455
references.citation: Biophys J. 2006 Dec 15;91(12):4490-9
references.pmid: 16997870
references.citation: Cell Motil Cytoskeleton. 1993;25(4):309-16
references.pmid: 8402952
references.citation: J Cell Biol. 1997 Aug 25;138(4):771-81
references.pmid: 9265645
references.citation: J Mol Biol. 2008 Sep 5;381(3):550-8
references.pmid: 18617188
references.citation: Trends Cell Biol. 2010 Apr;20(4):187-95
references.pmid: 20133134
references.citation: FEBS Lett. 2013 Apr 17;587(8):1215-9
references.pmid: 23395798
references.citation: Mol Cell. 2006 Nov 17;24(4):511-22
references.pmid: 17114056
references.citation: Biochemistry. 2009 Jan 20;48(2):370-8
references.pmid: 19113841
references.citation: FEBS Lett. 1995 Feb 27;360(2):111-4
references.pmid: 7875313
references.citation: J Cell Sci. 2011 Oct 1;124(Pt 19):3305-18
references.pmid: 21940796
references.citation: Biophys J. 2011 Jul 6;101(1):151-9
references.pmid: 21723825
references.citation: Biochemistry. 1993 Sep 28;32(38):9985-93
references.pmid: 8399167
references.citation: Mol Biol Cell. 2012 Sep;23(18):3707-21
references.pmid: 22855535
references.citation: Proc Natl Acad Sci U S A. 2011 Dec 20;108(51):20568-72
references.pmid: 22158895
references.citation: Biophys J. 2006 Jan 15;90(2):413-22
references.pmid: 16258044
references.citation: Biophys J. 2010 May 19;98(9):1893-901
references.pmid: 20441753
references.citation: Biophys J. 1999 Dec;77(6):2911-9
references.pmid: 10585915
references.citation: J Mol Biol. 2007 Feb 2;365(5):1350-8
references.pmid: 17134718
references.citation: Biophys Rev. 2009 May 15;1(2):51-59
references.pmid: 20700473
references.citation: J Mol Biol. 1982 Mar 15;155(4):409-28
references.pmid: 7086898
references.citation: Biophys J. 2010 May 19;98(10):2327-36
references.pmid: 20483342
references.citation: J Cell Biol. 2011 Oct 31;195(3):485-98
references.pmid: 22024167
references.citation: J Mol Biol. 2006 Aug 11;361(2):257-67
references.pmid: 16843490
references.citation: J Mol Biol. 2005 Feb 18;346(2):557-64
references.pmid: 15670604
references.citation: Proc Natl Acad Sci U S A. 2012 Oct 16;109(42):16923-7
references.pmid: 23027950
references.citation: J Mol Biol. 2005 Nov 11;353(5):990-1000
references.pmid: 16213521
references.citation: J Biol Chem. 2002 Nov 8;277(45):43011-6
references.pmid: 12055192
references.citation: Biochemistry. 1994 Dec 6;33(48):14387-92
references.pmid: 7981198
references.citation: J Cell Biol. 1990 Aug;111(2):453-63
references.pmid: 2143195
references.citation: Biochemistry. 1996 Nov 12;35(45):14054-61
references.pmid: 8916890
references.citation: J Biol Chem. 1998 Aug 14;273(33):20894-902
references.pmid: 9694836
references.citation: Nature. 2003 Sep 25;425(6956):423-7
references.pmid: 14508495