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ELife Feb 2023Actin isoforms organize into distinct networks that are essential for the normal function of eukaryotic cells. Despite a high level of sequence and structure...
Actin isoforms organize into distinct networks that are essential for the normal function of eukaryotic cells. Despite a high level of sequence and structure conservation, subtle differences in their design principles determine the interaction with myosin motors and actin-binding proteins. Therefore, identifying how the structure of actin isoforms relates to function is important for our understanding of normal cytoskeletal physiology. Here, we report the high-resolution structures of filamentous skeletal muscle α-actin (3.37 Å), cardiac muscle α-actin (3.07 Å), ß-actin (2.99 Å), and γ-actin (3.38 Å) in the Mg·ADP state with their native post-translational modifications. The structures revealed isoform-specific conformations of the N-terminus that shift closer to the filament surface upon myosin binding, thereby establishing isoform-specific interfaces. Collectively, the structures of single-isotype, post-translationally modified bare skeletal muscle α-actin, cardiac muscle α-actin, ß-actin, and γ-actin reveal general principles, similarities, and differences between isoforms. They complement the repertoire of known actin structures and allow for a comprehensive understanding of in vitro and in vivo functions of actin isoforms.
Topics: Actins; Protein Isoforms; Myosins; Muscle, Skeletal; Actin Cytoskeleton
PubMed: 36790143
DOI: 10.7554/eLife.82015 -
The Journal of Medical Investigation :... 2017The adherens junction (AJ) is a cadherin-based and actin filament associated cell-to-cell junction. AJs can contribute to tissue morphogenesis and homeostasis and their... (Review)
Review
The adherens junction (AJ) is a cadherin-based and actin filament associated cell-to-cell junction. AJs can contribute to tissue morphogenesis and homeostasis and their association with actin filaments is crucial for the functions. There are three types of AJs in terms of the mode of actin filament/AJ association. Among many actin-binding proteins associated with AJs, α-catenin is one of the most important actin filament/AJ linkers that functions in all types of AJs. Although α-catenin in cadherin-catenin complex appears to bind to actin filaments within cells, it fails to bind to actin filaments in vitro mysteriously. Recent report revealed that α-catenin in the complex can bind to actin filaments in vitro when forces are applied to the filament. In addition to force-sensitive vinculin binding, α-catenin has another force-sensitive property of actin filament-binding. Elucidation of its significance and the molecular mechanism is indispensable for understanding AJ formation and maintenance during tissue morphogenesis, function and repair. J. Med. Invest. 64: 14-19, February, 2017.
Topics: Actin Cytoskeleton; Actins; Adherens Junctions; Animals; Humans; Protein Binding; Protein Interaction Domains and Motifs; alpha Catenin
PubMed: 28373611
DOI: 10.2152/jmi.64.14 -
Journal of Biomolecular Structure &... May 2023Polymerization and depolymerization of actin play an essential role in eukaryotic cells. Actin exists in cells in both monomeric (G-actin) and filamentous (polymer,...
Polymerization and depolymerization of actin play an essential role in eukaryotic cells. Actin exists in cells in both monomeric (G-actin) and filamentous (polymer, F-actin) forms. Actin binding proteins (ABPs) facilitate the transition between these two states, and their interactions with these two states of actin are critical for actin-based cellular processes. Rapid depolymerization of actin is assisted in the brain and/or other cells by its oxidation by the enzyme Mical (yielding Mox-actin), and/or by the binding of Inverted Formin 2 (INF2) - which can also accelerate filaments formation. At their stoichiometric molar ratio INF2 and actin yield the 8S complex (consisting of 4 actin monomers: 2 INF2 dimer molecules). Using biochemical and biophysical methods, we investigate the structural arrangement of actin in the 8S particles and the interaction of INF2 with actin and Mox-actin. To that end, we show 2 D class averages of 8S particles obtained by negative staining electron microscopy. We also show that: (i) 8S particles can seed rapid actin assembly; (ii) Mox-actin and INF2 form 8S particles at proteins ratios similar to those of unoxidized actin; (iii) chemical crosslinkings suggest that actin monomers are in a parallel orientation in the 8S particles of both actin and Mox-actin; and (iv) INF2 accelerates the disassembly of Mox-F-actin. Our results provide better understanding of actin's arrangement in the 8S particles formed during actin depolymerization and in the early polymerization stages of both actin and Mox-actin.Communicated by Ramaswamy H. Sarma.
Topics: Actins; Formins; Microfilament Proteins; Actin Cytoskeleton
PubMed: 35343388
DOI: 10.1080/07391102.2022.2050947 -
Anatomical Record (Hoboken, N.J. : 2007) Dec 2018Actin is one of the most abundant intracellular proteins, essential in every eukaryotic cell type. Actin plays key roles in tissue morphogenesis, cell adhesion, muscle... (Review)
Review
Actin is one of the most abundant intracellular proteins, essential in every eukaryotic cell type. Actin plays key roles in tissue morphogenesis, cell adhesion, muscle contraction, and developmental reprogramming. Most actin studies have focused on its regulation at the protein level, either directly or through differential interactions with over a hundred intracellular binding partners. However, numerous studies emerging in recent years demonstrate specific types of nucleotide-level regulation that strongly affect non-muscle actins during cell migration and adhesion and are potentially applicable to other members of the actin family. This regulation involves zipcode-mediated actin mRNA targeting to the cell periphery, proposed to mediate local synthesis of actin at the cell leading edge, as well as the recently discovered N-terminal arginylation that specifically targets non-muscle β-actin via a nucleotide-dependent mechanism. Moreover, a study published this year suggests that actin's essential roles at the organismal level may be entirely nucleotide-dependent. This review summarizes the emerging data on actin's nucleotide-level regulation. Anat Rec, 301:1991-1998, 2018. © 2018 Wiley Periodicals, Inc.
Topics: Actin Cytoskeleton; Actins; Amino Acid Sequence; Animals; Humans; Protein Biosynthesis; Protein Processing, Post-Translational; RNA Interference
PubMed: 30312009
DOI: 10.1002/ar.23958 -
International Journal of Molecular... Mar 2022Ezrin is one of the members of the ezrin/radixin/moesin (ERM) family of proteins. It was originally discovered as an actin-binding protein in the microvilli structure... (Review)
Review
Ezrin is one of the members of the ezrin/radixin/moesin (ERM) family of proteins. It was originally discovered as an actin-binding protein in the microvilli structure about forty years ago. Since then, it has been revealed as a key protein with functions in a variety of fields including cell migration, survival, and signal transduction, as well as functioning as a structural component. Ezrin acts as a cross-linker of membrane proteins or phospholipids in the plasma membrane and the actin cytoskeleton. It also functions as a platform for signaling molecules at the cell surface. Moreover, ezrin is regarded as an important target protein in cancer diagnosis and therapy because it is a key protein involved in cancer progression and metastasis, and its high expression is linked to poor survival in many cancers. Small molecule inhibitors of ezrin have been developed and investigated as candidate molecules that suppress cancer metastasis. Here, we wish to comprehensively review the roles of ezrin from the pathophysiological points of view.
Topics: Actin Cytoskeleton; Actins; Cell Membrane; Cytoskeletal Proteins; Microfilament Proteins; Phosphoproteins
PubMed: 35328667
DOI: 10.3390/ijms23063246 -
Cytoskeleton (Hoboken, N.J.) Jun 2021The actin cytoskeleton is important for maintaining mechanical homeostasis in adherent cells, largely through its regulation of adhesion and cortical tension. The LIM... (Review)
Review
The actin cytoskeleton is important for maintaining mechanical homeostasis in adherent cells, largely through its regulation of adhesion and cortical tension. The LIM (Lin-11, Isl1, MEC-3) domain-containing proteins are involved in a myriad of cellular mechanosensitive pathways. Recent work has discovered that LIM domains bind to mechanically stressed actin filaments, suggesting a novel and widely conserved mechanism of mechanosensing. This review summarizes the current state of knowledge of LIM protein mechanosensitivity.
Topics: Actin Cytoskeleton; Actins; Biophysics; Cell Communication; LIM Domain Proteins; Protein Binding
PubMed: 34028199
DOI: 10.1002/cm.21677 -
ELife Nov 2023The MRTF-SRF pathway has been extensively studied for its crucial role in driving the expression of a large number of genes involved in actin cytoskeleton of various...
The MRTF-SRF pathway has been extensively studied for its crucial role in driving the expression of a large number of genes involved in actin cytoskeleton of various cell types. However, the specific contribution of MRTF-SRF in hair cells remains unknown. In this study, we showed that hair cell-specific deletion of or , but not a, leads to similar defects in the development of stereocilia dimensions and the maintenance of cuticular plate integrity. We used fluorescence-activated cell sorting-based hair cell RNA-Seq analysis to investigate the mechanistic underpinnings of the changes observed in and mutants, respectively. Interestingly, the transcriptome analysis revealed distinct profiles of genes regulated by and , suggesting different transcriptional regulation mechanisms of actin cytoskeleton activities mediated by and . Exogenous delivery of calponin 2 using Adeno-associated virus transduction in mutants partially rescued the impairments of stereocilia dimensions and the F-actin intensity of cuticular plate, suggesting the involvement of , as an downstream target, in regulating the hair bundle morphology and cuticular plate actin cytoskeleton organization. Our study uncovers, for the first time, the unexpected differential transcriptional regulation of actin cytoskeleton mediated by and in hair cells, and also demonstrates the critical role of SRF-CNN2 in modulating actin dynamics of the stereocilia and cuticular plate, providing new insights into the molecular mechanism underlying hair cell development and maintenance.
Topics: Hair Cells, Auditory; Actin Cytoskeleton; Stereocilia; Actins; Gene Expression Regulation
PubMed: 37982489
DOI: 10.7554/eLife.90155 -
European Journal of Cell Biology 2022Actin is among the most abundant proteins in eukaryotic cells and assembles into dynamic filamentous networks regulated by many actin binding proteins. The actin... (Review)
Review
Actin is among the most abundant proteins in eukaryotic cells and assembles into dynamic filamentous networks regulated by many actin binding proteins. The actin cytoskeleton must be finely tuned, both in space and time, to fulfill key cellular functions such as cell division, cell shape changes, phagocytosis and cell migration. While actin oxidation by reactive oxygen species (ROS) at non-physiological levels are known for long to impact on actin polymerization and on the cellular actin cytoskeleton, growing evidence shows that direct and reversible oxidation/reduction of specific actin amino acids plays an important and physiological role in regulating the actin cytoskeleton. In this review, we describe which actin amino acid residues can be selectively oxidized and reduced in many different ways (e.g. disulfide bond formation, glutathionylation, carbonylation, nitration, nitrosylation and other oxidations), the cellular enzymes at the origin of these post-translational modifications, and the impact of actin redox modifications both in vitro and in vivo. We show that the regulated balance of oxidation and reduction of key actin amino acid residues contributes to the control of actin filament polymerization and disassembly at the subcellular scale and highlight how improper redox modifications of actin can lead to pathological conditions.
Topics: Actin Cytoskeleton; Actins; Amino Acids; Microfilament Proteins; Oxidation-Reduction
PubMed: 35716426
DOI: 10.1016/j.ejcb.2022.151249 -
ELife Jul 2022Experiments using purified proteins reveal how the network of filaments that underlie cell movement becomes denser when pushing against a stronger mechanical force.
Experiments using purified proteins reveal how the network of filaments that underlie cell movement becomes denser when pushing against a stronger mechanical force.
Topics: Actin Cytoskeleton; Actin-Related Protein 2-3 Complex; Actins; Cell Movement; Cytoskeleton
PubMed: 35894589
DOI: 10.7554/eLife.81108 -
Communications Biology Sep 2023Actin, an important component of eukaryotic cell cytoskeleton, regulates cell shape and transport. The morphology and biochemical properties of actin filaments are...
Actin, an important component of eukaryotic cell cytoskeleton, regulates cell shape and transport. The morphology and biochemical properties of actin filaments are determined by their structure and protein-protein contacts. Crowded environments can organize filaments into bundles, but less is known about how they affect F-actin structure. This study used 2D IR spectroscopy and spectral calculations to examine how crowding and bundling impact the secondary structure and local environments in filaments and weakly or strongly bundled networks. The results reveal that bundling induces changes in actin's secondary structure, leading to a decrease in β-sheet and an increase in loop conformations. Strongly bundled networks exhibit a decrease in backbone solvent exposure, with less perturbed α-helices and nearly "locked" β-sheets. Similarly, the loops become less hydrated but maintain a dynamic environment. These findings highlight the role of loop structure in actin network morphology and stability under morphology control by PEG.
Topics: Actins; Actin Cytoskeleton; Protein Structure, Secondary; Cytoskeleton; Cell Shape
PubMed: 37660224
DOI: 10.1038/s42003-023-05274-3