-
Cytoskeleton (Hoboken, N.J.) Jan 2023
Topics: Actins; Binding Sites; Microfilament Proteins
PubMed: 36579710
DOI: 10.1002/cm.21739 -
Nature Nov 2022ATP-hydrolysis-coupled actin polymerization is a fundamental mechanism of cellular force generation. In turn, force and actin filament (F-actin) nucleotide state...
ATP-hydrolysis-coupled actin polymerization is a fundamental mechanism of cellular force generation. In turn, force and actin filament (F-actin) nucleotide state regulate actin dynamics by tuning F-actin's engagement of actin-binding proteins through mechanisms that are unclear. Here we show that the nucleotide state of actin modulates F-actin structural transitions evoked by bending forces. Cryo-electron microscopy structures of ADP-F-actin and ADP-P-F-actin with sufficient resolution to visualize bound solvent reveal intersubunit interfaces bridged by water molecules that could mediate filament lattice flexibility. Despite extensive ordered solvent differences in the nucleotide cleft, these structures feature nearly identical lattices and essentially indistinguishable protein backbone conformations that are unlikely to be discriminable by actin-binding proteins. We next introduce a machine-learning-enabled pipeline for reconstructing bent filaments, enabling us to visualize both continuous structural variability and side-chain-level detail. Bent F-actin structures reveal rearrangements at intersubunit interfaces characterized by substantial alterations of helical twist and deformations in individual protomers, transitions that are distinct in ADP-F-actin and ADP-P-F-actin. This suggests that phosphate rigidifies actin subunits to alter the bending structural landscape of F-actin. As bending forces evoke nucleotide-state dependent conformational transitions of sufficient magnitude to be detected by actin-binding proteins, we propose that actin nucleotide state can serve as a co-regulator of F-actin mechanical regulation.
Topics: Actin Cytoskeleton; Actins; Adenosine Diphosphate; Cryoelectron Microscopy; Microfilament Proteins; Solvents; Machine Learning; Protein Conformation
PubMed: 36289330
DOI: 10.1038/s41586-022-05366-w -
Cells Oct 2020The actin cytoskeleton plays a crucial role in many cellular processes while its reorganization is important in maintaining cell homeostasis. However, in the case of... (Review)
Review
The actin cytoskeleton plays a crucial role in many cellular processes while its reorganization is important in maintaining cell homeostasis. However, in the case of cancer cells, actin and ABPs (actin-binding proteins) are involved in all stages of carcinogenesis. Literature has reported that ABPs such as SATB1 (special AT-rich binding protein 1), WASP (Wiskott-Aldrich syndrome protein), nesprin, and villin take part in the initial step of carcinogenesis by regulating oncogene expression. Additionally, changes in actin localization promote cell proliferation by inhibiting apoptosis (SATB1). In turn, migration and invasion of cancer cells are based on the formation of actin-rich protrusions (Arp2/3 complex, filamin A, fascin, α-actinin, and cofilin). Importantly, more and more scientists suggest that microfilaments together with the associated proteins mediate tumor vascularization. Hence, the presented article aims to summarize literature reports in the context of the potential role of actin and ABPs in all steps of carcinogenesis.
Topics: Actins; Carcinogenesis; Cell Movement; Humans; Microfilament Proteins
PubMed: 33036298
DOI: 10.3390/cells9102245 -
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 FEBS Journal Mar 2021Fascin is an F-actin-bundling protein that cross-links individual actin filaments into straight and stiff bundles. Fascin overexpression in cancer is strongly associated... (Review)
Review
Fascin is an F-actin-bundling protein that cross-links individual actin filaments into straight and stiff bundles. Fascin overexpression in cancer is strongly associated with poor prognosis and metastatic progression across different cancer types. It is well established that fascin plays a causative role in promoting metastatic progression. We will review the recent progress in our understanding of mechanisms underlying fascin-mediated cancer metastasis. This review will cover the biochemical basis for fascin-bundling activity, the mechanisms by which cancer cells upregulate fascin expression and the mechanism underlying fascin-mediated cancer cell migration, invasion, and metastatic colonization. We propose that fascin has broad roles in both metastatic dissemination and metastatic colonization. Understanding these mechanisms will be crucial to the development of anti-metastasis therapeutics targeting fascin.
Topics: Actin Cytoskeleton; Actins; Animals; Carrier Proteins; Cell Movement; Cell Proliferation; Gene Expression Regulation, Neoplastic; Humans; Microfilament Proteins; Neoplasm Metastasis; Neoplasm Proteins; Neoplasms; Neoplastic Cells, Circulating; Protein Isoforms; Signal Transduction; Transcription, Genetic; Tumor Microenvironment
PubMed: 32657526
DOI: 10.1111/febs.15484 -
Pediatric Allergy and Immunology :... Apr 2023Immunoactinopathies caused by mutations in actin-related proteins are a growing group of inborn errors of immunity (IEI). Immunoactinopathies are caused by a... (Review)
Review
Immunoactinopathies caused by mutations in actin-related proteins are a growing group of inborn errors of immunity (IEI). Immunoactinopathies are caused by a dysregulated actin cytoskeleton and affect hematopoietic cells especially because of their unique capacity to survey the body for invading pathogens and altered self, such as cancer cells. These cell motility and cell-to-cell interaction properties depend on the dynamic nature of the actin cytoskeleton. Wiskott-Aldrich syndrome (WAS) is the archetypical immunoactinopathy and the first described. WAS is caused by loss-of-function and gain-of-function mutations in the actin regulator WASp, uniquely expressed in hematopoietic cells. Mutations in WAS cause a profound disturbance of actin cytoskeleton regulation of hematopoietic cells. Studies during the last 10 years have shed light on the specific effects on different hematopoietic cells, revealing that they are not affected equally by mutations in the WAS gene. Moreover, the mechanistic understanding of how WASp controls nuclear and cytoplasmatic activities may help to find therapeutic alternatives according to the site of the mutation and clinical phenotypes. In this review, we summarize recent findings that have added to the complexity and increased our understanding of WAS-related diseases and immunoactinopathies.
Topics: Humans; Actins; Wiskott-Aldrich Syndrome; Mutation; Phenotype
PubMed: 37102395
DOI: 10.1111/pai.13951 -
Cellular Microbiology Apr 2021Salmonella enterica serovars infect a broad range of mammalian hosts including humans, causing both gastrointestinal and systemic diseases. Following uptake into host... (Review)
Review
Salmonella enterica serovars infect a broad range of mammalian hosts including humans, causing both gastrointestinal and systemic diseases. Following uptake into host cells, bacteria replicate within vacuoles (Salmonella-containing vacuoles; SCVs). Clusters of SCVs are frequently associated with a meshwork of F-actin. This meshwork is dependent on the Salmonella pathogenicity island 2 encoded type III secretion system and its effector SteC. SteC contains a region with weak similarity to conserved subdomains of eukaryotic kinases and has kinase activity that is required for the formation of the F-actin meshwork. Several substrates of SteC have been identified. In this mini-review, we attempt to integrate these findings and propose a more unified model to explain SCV-associated F-actin: SteC (i) phosphorylates the actin sequestering protein Hsp27, which increases the local G-actin concentration (ii) binds to and phosphorylates formin family FMNL proteins, which enables actin polymerisation and (iii) phosphorylates MEK, resulting in activation of the MEK/ERK/MLCK/Myosin II pathway, leading to F-actin bundling. We also consider the possible physiological functions of SCV-associated F-actin and similar structures produced by other intracellular bacterial pathogens.
Topics: Actin Cytoskeleton; Actins; Animals; Epithelial Cells; Genomic Islands; Host-Pathogen Interactions; Humans; Mice; Phosphorylation; Salmonella enterica; Shiga-Toxigenic Escherichia coli; Vacuoles
PubMed: 33534187
DOI: 10.1111/cmi.13315 -
International Journal of Molecular... May 2020Actin is a widely expressed protein found in almost all eukaryotic cells. In humans, there are six different genes, which encode specific actin isoforms. Disease-causing... (Review)
Review
Actin is a widely expressed protein found in almost all eukaryotic cells. In humans, there are six different genes, which encode specific actin isoforms. Disease-causing mutations have been described for each of these, most of which are missense. Analysis of the position of the resulting mutated residues in the protein reveals mutational hotspots. Many of these occur in regions important for actin polymerization. We briefly discuss the challenges in characterizing the effects of these actin mutations, with a focus on cardiac actin mutations.
Topics: Actins; Animals; Humans; Muscle, Skeletal; Muscular Diseases; Mutation, Missense; Myocardium; Myosins; Polymerization; Protein Isoforms
PubMed: 32397632
DOI: 10.3390/ijms21093371 -
Nature Communications Jun 2023The actin cytoskeleton is of fundamental importance for cellular structure and plasticity. However, abundance and function of filamentous actin in the nucleus are still...
The actin cytoskeleton is of fundamental importance for cellular structure and plasticity. However, abundance and function of filamentous actin in the nucleus are still controversial. Here we show that the actin-based molecular motor myosin VI contributes to the stabilization of stalled or reversed replication forks. In response to DNA replication stress, myosin VI associates with stalled replication intermediates and cooperates with the AAA ATPase Werner helicase interacting protein 1 (WRNIP1) in protecting these structures from DNA2-mediated nucleolytic attack. Using functionalized affinity probes to manipulate myosin VI levels in a compartment-specific manner, we provide evidence for the direct involvement of myosin VI in the nucleus and against a contribution of the abundant cytoplasmic pool during the replication stress response.
Topics: DNA Replication; DNA-Binding Proteins; Actins; Cell Nucleus
PubMed: 37355687
DOI: 10.1038/s41467-023-39517-y -
International Journal of Molecular... Sep 2023Quantum dots (QDs) are a type of nanoparticle with excellent optical properties, suitable for many optical-based biomedical applications. However, the potential of...
Quantum dots (QDs) are a type of nanoparticle with excellent optical properties, suitable for many optical-based biomedical applications. However, the potential of quantum dots to be used in clinical settings is limited by their toxicity. As such, much effort has been invested to examine the mechanism of QDs' toxicity. Yet, the current literature mainly focuses on ROS- and apoptosis-mediated cell death induced by QDs, which overlooks other aspects of QDs' toxicity. Thus, our study aimed to provide another way by which QDs negatively impact cellular processes by investigating the possibility of protein structure and function modification upon direct interaction. Through shotgun proteomics, we identified a number of QD-binding proteins, which are functionally associated with essential cellular processes and components, such as transcription, translation, vesicular trafficking, and the actin cytoskeleton. Among these proteins, we chose to closely examine the interaction between quantum dots and actin, as actin is one of the most abundant proteins in cells and plays crucial roles in cellular processes and structural maintenance. We found that CdSe/ZnS QDs spontaneously bind to G-actin in vitro, causing a static quenching of G-actin's intrinsic fluorescence. Furthermore, we found that this interaction favors the formation of a QD-actin complex with a binding ratio of 1:2.5. Finally, we also found that CdSe/ZnS QDs alter the secondary structure of G-actin, which may affect G-actin's function and properties. Overall, our study provides an in-depth mechanistic examination of the impact of CdSe/ZnS QDs on G-actin, proposing that direct interaction is another aspect of QDs' toxicity.
Topics: Actins; Quantum Dots; Zinc Compounds; Sulfides; Selenium Compounds
PubMed: 37834208
DOI: 10.3390/ijms241914760