Regulation of cytoskeletal dynamics by actin-monomer-binding proteins

Paavilainen, Ville O.; Bertling, Enni; Falck, S. von; Lappalainen, Pekka

doi:10.1016/j.tcb.2004.05.002

Cited by 227 publications

(228 citation statements)

References 81 publications

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“…It will prove interesting to determine whether unpolymerized MreB has an inherent affinity for the phospholipid membrane or for specific membrane-bound proteins. Alternatively, it remains a possibility that unpolymerized MreB is not membrane-associated but instead interacts with a larger protein complex that could function to sequester MreB or exchange its nucleotide, much as CAP (cyclase-associated protein) or profilin function for eukaryotic actin (42).…”

Section: Unpolymerized Mreb Does Not Behave Like a Free Cytoplasmic Pro-mentioning

confidence: 99%

Single molecules of the bacterial actin MreB undergo directed treadmilling motion in Caulobacter crescentus

Kim

Gitai

Kinkhabwala

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

194

241

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The actin cytoskeleton represents a key regulator of multiple essential cellular functions in both eukaryotes and prokaryotes. In eukaryotes, these functions depend on the orchestrated dynamics of actin filament assembly and disassembly. However, the dynamics of the bacterial actin homolog MreB have yet to be examined in vivo. In this study, we observed the motion of single fluorescent MreB-yellow fluorescent protein fusions in living Caulobacter cells in a background of unlabeled MreB. With time-lapse imaging, polymerized MreB [filamentous MreB (fMreB)] and unpolymerized MreB [globular MreB (gMreB)] monomers could be distinguished: gMreB showed fast motion that was characteristic of Brownian diffusion, whereas the labeled molecules in fMreB displayed slow, directed motion. This directional movement of labeled MreB in the growing polymer provides an indication that, like actin, MreB monomers treadmill through MreB filaments by preferential polymerization at one filament end and depolymerization at the other filament end. From these data, we extract several characteristics of single MreB filaments, including that they are, on average, much shorter than the cell length and that the direction of their polarized assembly seems to be independent of the overall cellular polarity. Thus, MreB, like actin, exhibits treadmilling behavior in vivo, and the long MreB structures that have been visualized in multiple bacterial species seem to represent bundles of short filaments that lack a uniform global polarity.bacteria ͉ cytoskeleton ͉ single-molecule fluorescence I n both eukaryotic and prokaryotic cells, actin mediates essential cellular processes. A quantitative understanding of the kinetic dynamics and ultrastructural architecture of actin's polymerized filaments has helped elucidate the mechanisms by which eukaryotic actin functions. For example, high-resolution imaging and the in vivo and in vitro dissection of the kinetics of its assembly have demonstrated how actin polymerization at the tips of a rigid, crosslinked actin meshwork can drive cell motility at the leading edge of Dictyostelium (1, 2). In budding yeast, the polarized assembly of actin cables provides both a road and direction signs for the directed transport of proteins to the tip of growing buds (3).There are two known bacterial actin homologs, the widely conserved, chromosomally encoded MreB family of proteins and the plasmid-specific ParM family of proteins. ParM functions to partition plasmid DNA by polymerizing in between two sister plasmids, thereby generating a tension rod that physically pushes them apart (4). MreB is essential in most bacteria and has been shown to form a lengthwise spiral that contributes to cell shape, chromosome segregation, and polar protein localization in multiple species, including Caulobacter crescentus, Escherichia coli, and Bacillus subtilis (5-10). The mechanism by which MreB executes its functions remains largely unknown (11).In vitro studies of the dynamics of eukaryotic actin filament assembly have demonstrated th...

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Section: Unpolymerized Mreb Does Not Behave Like a Free Cytoplasmic Pro-mentioning

confidence: 99%

Single molecules of the bacterial actin MreB undergo directed treadmilling motion in Caulobacter crescentus

Kim

Gitai

Kinkhabwala

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

194

241

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“…However, these regions, and especially the long ␣ -helix, are less conserved in coactosin and Abp1, which bind F-actin with relatively low affi nity and do not interact with G-actin or induce fi lament disassembly (Table S1, avail- plex with Twf-C, profi lin, gelsolin-S1, and ciboulot WH2 domains (all of which were crystallized without DNase I bound to subdomains 2 and 4) reveals that in complexes that inhibit nucleotide exchange, the cleft between actin subdomains 2 and 4 is in a " closed " state. In contrast, in the profi lin -actin complex, Paavilainen et al, 2004 ). Also, the isolated C-terminal ADF-H domain of twinfilin binds G-actin with high affinity and efficiently inhibits G-actin nucleotide exchange (Fig.…”

mentioning

confidence: 99%

Structure of the actin-depolymerizing factor homology domain in complex with actin

Paavilainen

Oksanen

Goldman

et al. 2008

The Journal of Cell Biology

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150

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Abbreviations used in this paper: ADF-H, actin-depolymerizing factor homology; NBD, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole; WH2, WASP homology 2.The online version of this paper contains supplemental material. IntroductionPolymerization of actin fi laments against membranes produces pushing forces that are required for various cellular processes such as motility, morphogenesis, and endocytosis ( Pollard and Borisy, 2003 ;Kaksonen et al., 2006 ). Despite the large number of proteins regulating actin dynamics, many of them interact with actin through a relatively small number of protein domains. Among the central actin-binding domains is the actin-depolymerizing factor homology (ADF-H) domain, which occurs in five functionally distinct classes of proteins: ADF/cofilin, twinfi lin, Abp1/drebrin, coactosin, and glia maturation factor ( Paavilainen et al., 2007 ).The founding member of this family, ADF/cofi lin, binds both monomeric and fi lamentous actin, preferably in the ADPbound form, and induces a structural rearrangement in the actin fi lament that leads to its disassembly. When bound to an actin monomer, ADF/cofi lin inhibits spontaneous nucleotide exchange ( Carlier et al., 1997 ;Bamburg, 1999 ;Andrianantoandro and Pollard, 2006 ). In cells, ADF/cofi lin plays an essential role in various processes by promoting disassembly of aged actin fi laments ( Okreglak and Drubin, 2007 ). In contrast to ADF/cofi lin, which consists of a single ADF-H domain, twinfi lin is composed of two ADF-H domains separated by a short linker region . Twinfi lin binds ADP-actin monomers and fi lament barbed ends with high affi nity, and prevents monomer assembly into fi lament ends Helfer et al., 2006 ). In addition, yeast twinfi lin induces fi lament severing at a low pH ( Moseley et al., 2006 ). Biochemical studies suggested that during barbedend capping, twinfi lin ' s N-terminal ADF-H domain interacts with the terminal actin subunit, whereas the C-terminal ADF-H domain binds to the side of an actin fi lament through a similar mechanism to that of ADF/cofi lin ( Paavilainen et al., 2007 ). The exact functions of the Abp1/drebrin, coactosin, and glia maturation factor are less well understood, although also these proteins are linked to regulation of actin dynamics ( de Hostos et al., 1993 ;Quintero-Monzon et al., 2005 ;Ikeda et al., 2006 ).Although the biochemical activities and cellular functions of ADF-H domain proteins are rapidly being uncovered, the structure of an ADF-H domain in complex with actin has not been reported. Indirect structural methods have provided controversial results, and even the binding site of this domain on actin is not known ( Wriggers et al., 1998 ;Kamal et al., 2007 ). Consequently, the structural mechanisms by which twinfi lin and ADF/cofi lin inhibit nucleotide exchange on actin monomers and how ADF/cofi lin induces fi lament depolymerization/ severing are unknown.A ctin dynamics provide the driving force for many cellular processes including motility and endocytosis. Among the central cytoskeletal re...

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“…The conserved protein cofilin is one of the most important regulators of actin filament disassembly Welch and Mullins 2002;Balcer et al 2003;Paavilainen et al 2004). Despite extensive research some disagreement remains as to the biochemical mechanism by which cofilin promotes actin filament disassembly.…”

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confidence: 99%

The flare Gene, Which Encodes the AIP1 Protein of Drosophila, Functions to Regulate F-Actin Disassembly in Pupal Epidermal Cells

2007

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Adult Drosophila are decorated with several types of polarized cuticular structures, such as hairs and bristles. The morphogenesis of these takes place in pupal cells and is mediated by the actin and microtubule cytoskeletons. Mutations in flare ( flr) result in grossly abnormal epidermal hairs. We report here that flr encodes the Drosophila actin interacting protein 1 (AIP1). In other systems this protein has been found to promote cofilin-mediated F-actin disassembly. In Drosophila cofilin is encoded by twinstar (tsr). We show that flr mutations result in increased levels of F-actin accumulation and increased F-actin stability in vivo. Further, flr is essential for cell proliferation and viability and for the function of the frizzled planar cell polarity system. All of these phenotypes are similar to those seen for tsr mutations. This differs from the situation in yeast where cofilin is essential while aip1 mutations result in only subtle defects in the actin cytoskeleton. Surprisingly, we found that mutations in flr and tsr also result in greatly increased tubulin staining, suggesting a tight linkage between the actin and microtubule cytoskeleton in these cells.T HE actin cytoskeleton plays conserved and key roles in a variety of cellular activities in eukaryotes, such as cell migration, endocytosis, cytokinesis, and cell shape changes

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Regulation of cytoskeletal dynamics by actin-monomer-binding proteins

Cited by 227 publications

References 81 publications

Single molecules of the bacterial actin MreB undergo directed treadmilling motion in Caulobacter crescentus

Single molecules of the bacterial actin MreB undergo directed treadmilling motion in Caulobacter crescentus

Structure of the actin-depolymerizing factor homology domain in complex with actin

The flare Gene, Which Encodes the AIP1 Protein of Drosophila, Functions to Regulate F-Actin Disassembly in Pupal Epidermal Cells

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