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Journal of Cell Science Jan 2018Globular (G)-actin, the actin monomer, assembles into polarized filaments that form networks that can provide structural support, generate force and organize the cell.... (Review)
Review
Globular (G)-actin, the actin monomer, assembles into polarized filaments that form networks that can provide structural support, generate force and organize the cell. Many of these structures are highly dynamic and to maintain them, the cell relies on a large reserve of monomers. Classically, the G-actin pool has been thought of as homogenous. However, recent work has shown that actin monomers can exist in distinct groups that can be targeted to specific networks, where they drive and modify filament assembly in ways that can have profound effects on cellular behavior. This Review focuses on the potential factors that could create functionally distinct pools of actin monomers in the cell, including differences between the actin isoforms and the regulation of G-actin by monomer binding proteins, such as profilin and thymosin β4. Owing to difficulties in studying and visualizing G-actin, our knowledge over the precise role that specific actin monomer pools play in regulating cellular actin dynamics remains incomplete. Here, we discuss some of these unanswered questions and also provide a summary of the methodologies currently available for the imaging of G-actin.
Topics: Actins; Animals; Cytoskeleton; Humans; Kinetics; Models, Molecular; Profilins; Thymosin
PubMed: 29321224
DOI: 10.1242/jcs.203760 -
Cold Spring Harbor Perspectives in... Jul 2017Cell adhesions link cells to the extracellular matrix (ECM) and to each other and depend on interactions with the actin cytoskeleton. Both cell-ECM and cell-cell... (Review)
Review
Cell adhesions link cells to the extracellular matrix (ECM) and to each other and depend on interactions with the actin cytoskeleton. Both cell-ECM and cell-cell adhesion sites contain discrete, yet overlapping, functional modules. These modules establish physical associations with the actin cytoskeleton, locally modulate actin organization and dynamics, and trigger intracellular signaling pathways. Interplay between these modules generates distinct actin architectures that underlie different stages, types, and functions of cell-ECM and cell-cell adhesions. Actomyosin contractility is required to generate mature, stable adhesions, as well as to sense and translate the mechanical properties of the cellular environment into changes in cell organization and behavior. Here, we review the organization and function of different adhesion modules and how they interact with the actin cytoskeleton. We highlight the molecular mechanisms of mechanotransduction in adhesions and how adhesion molecules mediate cross talk between cell-ECM and cell-cell adhesion sites.
Topics: Actins; Cell Adhesion; Cell Communication; Extracellular Matrix; Mechanotransduction, Cellular; Signal Transduction
PubMed: 28679638
DOI: 10.1101/cshperspect.a023234 -
Histochemistry and Cell Biology Nov 2020Actin is a conserved cytoskeletal protein with essential functions. Here, we review the state-of-the-art reagents, tools and methods used to probe actin biology and... (Review)
Review
Actin is a conserved cytoskeletal protein with essential functions. Here, we review the state-of-the-art reagents, tools and methods used to probe actin biology and functions in zebrafish embryo and larvae. We also discuss specific cell types and tissues where the study of actin in zebrafish has provided new insights into its functions.
Topics: Actins; Animals; Zebrafish
PubMed: 33095903
DOI: 10.1007/s00418-020-01932-3 -
Structure (London, England : 1993) Jul 2010Actin works within eukaryotic cells to facilitate a variety of cellular processes, which are driven by the assembly of G-actin (monomeric form) into F-actin (fibrous... (Review)
Review
Actin works within eukaryotic cells to facilitate a variety of cellular processes, which are driven by the assembly of G-actin (monomeric form) into F-actin (fibrous form), and the disassembly of F-actin into G-actin. F-actin adopts multiple conformations, which are specified by interactions with various actin-binding proteins. Knowledge of the multiple conformations of actin is the key for understanding its cellular functions. Recently, we published a refined model for F-actin. In this review, based on this model, we discuss the origin, mechanism, and possible physiological significance of the multiple conformations of F-actin.
Topics: Actins; Models, Molecular; Protein Binding; Protein Conformation; Thermodynamics
PubMed: 20637412
DOI: 10.1016/j.str.2010.05.009 -
Annual Review of Biophysics 2015The actin cytoskeleton is essential for diverse processes in mammalian cells; these processes range from establishing cell polarity to powering cell migration to driving... (Review)
Review
The actin cytoskeleton is essential for diverse processes in mammalian cells; these processes range from establishing cell polarity to powering cell migration to driving cytokinesis to positioning intracellular organelles. How these many functions are carried out in a spatiotemporally regulated manner in a single cytoplasm has been the subject of much study in the cytoskeleton field. Recent work has identified a host of actin nucleation factors that can build architecturally diverse actin structures. The biochemical properties of these factors, coupled with their cellular location, likely define the functional properties of actin structures. In this article, we describe how recent advances in cell biology and biochemistry have begun to elucidate the role of individual actin nucleation factors in generating distinct cellular structures. We also consider how the localization and orientation of actin nucleation factors, in addition to their kinetic properties, are critical to their ability to build a functional actin cytoskeleton.
Topics: Actin Cytoskeleton; Actins; Animals; Cell Movement; Endocytosis; Microfilament Proteins; Pseudopodia
PubMed: 26098516
DOI: 10.1146/annurev-biophys-060414-034308 -
Journal of Molecular Biology Jan 2000Two factors have limited studies of the properties of nucleotide-free actin (NFA). First, actin lacking bound nucleotide denatures rapidly without stabilizing agents...
Two factors have limited studies of the properties of nucleotide-free actin (NFA). First, actin lacking bound nucleotide denatures rapidly without stabilizing agents such as sucrose; and second, without denaturants such as urea, it is difficult to remove all of the bound nucleotide. We used apyrase, EDTA and Dowex-1 to prepare actin that is stable in sucrose and approximately 99 % free of bound nucleotide. In high concentrations of sucrose where NFA is stable, it polymerizes more favorably with a lag phase shorter than ATP-actin and a critical concentration close to zero. NFA filaments are stable, but depolymerize at low sucrose concentrations due to denaturation of subunits when they dissociate from filament ends. By electron microscopy of negatively stained specimens, NFA forms long filaments with a persistence length 1.5 times greater than ADP-actin filaments. Three-dimensional helical reconstructions of NFA and ADP-actin filaments at 2.5 nm resolution reveal similar intersubunit contacts along the two long-pitch helical strands but statistically significant less mass density between the two strands of NFA filaments. When compared with ADP-actin filaments, the major difference peak of NFA filaments is near, but does not coincide with, the vacated nucleotide binding site. The empty nucleotide binding site in these NFA filaments is not accessible to free nucleotide in the solution. The affinity of NFA filaments for rhodamine phalloidin is lower than that of native actin filaments, due to a lower association rate. This work confirms that bound nucleotide is not essential for actin polymerization, so the main functions of the nucleotide are to stabilize monomers, modulate the mechanical and dynamic properties of filaments through ATP hydrolysis and phosphate release, and to provide an internal timer for the age of the filament.
Topics: Actins; Adenosine Diphosphate; Biopolymers; Chromatography, High Pressure Liquid; Kinetics; Ligands; Microscopy, Electron; Protein Conformation
PubMed: 10623543
DOI: 10.1006/jmbi.1999.3390 -
Biochemistry Oct 2013For many years, bacteria were considered rather simple organisms, but the dogmatic notion that subcellular organization is a eukaryotic trait has been overthrown for... (Review)
Review
For many years, bacteria were considered rather simple organisms, but the dogmatic notion that subcellular organization is a eukaryotic trait has been overthrown for more than a decade. The discovery of homologues of the eukaryotic cytoskeletal proteins actin, tubulin, and intermediate filaments in bacteria has been instrumental in changing this view. Over the past few years, we have gained an incredible level of insight into the diverse family of bacterial actins and their molecular workings. Here we review the functional, biochemical, and structural features of the most well-studied bacterial actins.
Topics: Actins; Adenosine Triphosphatases; Bacteria; Bacterial Proteins; Cytoskeleton; Escherichia coli Proteins; Phylogeny
PubMed: 24015924
DOI: 10.1021/bi4010792 -
Protein Science : a Publication of the... May 2023Palladin is an actin binding protein that is specifically upregulated in metastatic cancer cells but also colocalizes with actin stress fibers in normal cells and is...
Palladin is an actin binding protein that is specifically upregulated in metastatic cancer cells but also colocalizes with actin stress fibers in normal cells and is critical for embryonic development as well as wound healing. Of nine isoforms present in humans, only the 90 kDa isoform of palladin, comprising three immunoglobulin (Ig) domains and one proline-rich region, is ubiquitously expressed. Previous work has established that the Ig3 domain of palladin is the minimal binding site for F-actin. In this work, we compare functions of the 90 kDa isoform of palladin to the isolated actin binding domain. To understand the mechanism of action for how palladin can influence actin assembly, we monitored F-actin binding and bundling as well as actin polymerization, depolymerization, and copolymerization. Together, these results demonstrate that there are key differences between the Ig3 domain and full-length palladin in actin binding stoichiometry, polymerization, and interactions with G-actin. Understanding the role of palladin in regulating the actin cytoskeleton may help us develop means to prevent cancer cells from reaching the metastatic stage of cancer progression.
Topics: Humans; Actins; Cytoskeletal Proteins; Microfilament Proteins; Actin Cytoskeleton; Protein Isoforms; Phosphoproteins
PubMed: 37027210
DOI: 10.1002/pro.4638 -
The Journal of Cell Biology Nov 2023The c-Jun N-terminal kinase (JNK) regulates various important physiological processes. Although the JNK pathway has been under intense investigation for over 20 yr, its...
The c-Jun N-terminal kinase (JNK) regulates various important physiological processes. Although the JNK pathway has been under intense investigation for over 20 yr, its complexity is still perplexing, with multiple protein partners underlying the diversity of its activity. We show that JNK is associated with the basal bodies in both primary and motile cilia. Loss of JNK disrupts basal body migration and docking and leads to severe ciliogenesis defects. JNK's involvement in ciliogenesis stems from a dual role in the regulation of the actin networks of multiciliated cells (MCCs) and the establishment of the intraflagellar transport-B core complex. JNK signaling is also critical for the maintenance of the actin networks and ciliary function in mature MCCs. JNK is implicated in the development of diabetes, neurodegeneration, and liver disease, all of which have been linked to ciliary dysfunction. Our work uncovers a novel role of JNK in ciliogenesis and ciliary function that could have important implications for JNK's role in the disease.
Topics: Actins; Cilia; MAP Kinase Signaling System; Phosphorylation; Protein Processing, Post-Translational; JNK Mitogen-Activated Protein Kinases
PubMed: 37851005
DOI: 10.1083/jcb.202303052 -
Current Opinion in Cell Biology Feb 2013Now that many genomes have been sequenced, a central concern of cell biology is to understand how the proteins they encode work together to create living matter. In... (Review)
Review
Now that many genomes have been sequenced, a central concern of cell biology is to understand how the proteins they encode work together to create living matter. In vitro studies form an essential part of this program because understanding cellular functions of biological molecules often requires isolating them and reconstituting their activities. In particular, many elements of the actin cytoskeleton were first discovered by biochemical methods and their cellular functions deduced from in vitro experiments. We highlight recent advances that have come from in vitro studies, beginning with studies of actin filaments, and ending with multi-component reconstitutions of complex actin-based processes, including force-generation and cell spreading. We describe both scientific results and the technical innovations that made them possible.
Topics: Actin Cytoskeleton; Actins; Biomimetic Materials; Cell Shape; Movement
PubMed: 23267766
DOI: 10.1016/j.ceb.2012.11.007