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Biophysical Journal Oct 2021We used computational methods to analyze the mechanism of actin filament nucleation. We assumed a pathway where monomers form dimers, trimers, and tetramers that then...
We used computational methods to analyze the mechanism of actin filament nucleation. We assumed a pathway where monomers form dimers, trimers, and tetramers that then elongate to form filaments but also considered other pathways. We aimed to identify the rate constants for these reactions that best fit experimental measurements of polymerization time courses. The analysis showed that the formation of dimers and trimers is unfavorable because the association reactions are orders of magnitude slower than estimated in previous work rather than because of rapid dissociation of dimers and trimers. The 95% confidence intervals calculated for the four rate constants spanned no more than one order of magnitude. Slow nucleation reactions are consistent with published high-resolution structures of actin filaments and molecular dynamics simulations of filament ends. One explanation for slow dimer formation, which we support with computational analysis, is that actin monomers are in a conformational equilibrium with a dominant conformation that cannot participate in the nucleation steps.
Topics: Actin Cytoskeleton; Actins; Cytoskeleton; Kinetics; Polymerization
PubMed: 34509503
DOI: 10.1016/j.bpj.2021.09.006 -
The Journal of Cell Biology Dec 2023Understanding how numerous actin-binding proteins (ABPs) work in concert to control the assembly, organization, and turnover of the actin cytoskeleton requires...
Understanding how numerous actin-binding proteins (ABPs) work in concert to control the assembly, organization, and turnover of the actin cytoskeleton requires quantitative information about the levels of each component. Here, we measured the cellular concentrations of actin and the majority of the conserved ABPs in Saccharomyces cerevisiae, as well as the free (cytosolic) fractions of each ABP. The cellular concentration of actin is estimated to be 13.2 µM, with approximately two-thirds in the F-actin form and one-third in the G-actin form. Cellular concentrations of ABPs range from 12.4 to 0.85 µM (Tpm1> Pfy1> Cof1> Abp1> Srv2> Abp140> Tpm2> Aip1> Cap1/2> Crn1> Sac6> Twf1> Arp2/3> Scp1). The cytosolic fractions of all ABPs are unexpectedly high (0.6-0.9) and remain so throughout the cell cycle. Based on these numbers, we speculate that F-actin binding sites are limited in vivo, which leads to high cytosolic levels of ABPs, and in turn helps drive the rapid assembly and turnover of cellular F-actin structures.
Topics: Actin Cytoskeleton; Actins; Microfilament Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Cytosol
PubMed: 37801069
DOI: 10.1083/jcb.202306036 -
Current Opinion in Plant Biology Jun 2023Plants have developed fine-tuned cellular mechanisms to respond to a variety of intracellular and extracellular signals. These responses often necessitate the... (Review)
Review
Plants have developed fine-tuned cellular mechanisms to respond to a variety of intracellular and extracellular signals. These responses often necessitate the rearrangement of the plant cytoskeleton to modulate cell shape and/or to guide vesicle trafficking. At the cell periphery, both actin filaments and microtubules associate with the plasma membrane that acts as an integrator of the intrinsic and extrinsic environments. At this membrane, acidic phospholipids such as phosphatidic acid, and phosphoinositides contribute to the selection of peripheral proteins and thereby regulate the organization and dynamic of the actin and microtubules. After recognition of the importance of phosphatidic acid on cytoskeleton dynamics and rearrangement, it became apparent that the other lipids might play a specific role in shaping the cytoskeleton. This review focuses on the emerging role of the phosphatidylinositol 4,5-bisphosphate for the regulation of the peripherical cytoskeleton during cellular processes such as cytokinesis, polar growth, biotic and abiotic responses.
Topics: Phosphatidylinositols; Cytoskeleton; Microtubules; Actins; Cell Membrane; Actin Cytoskeleton; Plants
PubMed: 37084498
DOI: 10.1016/j.pbi.2023.102365 -
Cells Jun 2021The scaffolding protein family Fe65, composed of Fe65, Fe65L1, and Fe65L2, was identified as an interaction partner of the amyloid precursor protein (APP), which plays a... (Review)
Review
The scaffolding protein family Fe65, composed of Fe65, Fe65L1, and Fe65L2, was identified as an interaction partner of the amyloid precursor protein (APP), which plays a key function in Alzheimer's disease. All three Fe65 family members possess three highly conserved interaction domains, forming complexes with diverse binding partners that can be assigned to different cellular functions, such as transactivation of genes in the nucleus, modulation of calcium homeostasis and lipid metabolism, and regulation of the actin cytoskeleton. In this article, we rule out putative new intracellular signaling mechanisms of the APP-interacting protein Fe65 in the regulation of actin cytoskeleton dynamics in the context of various neuronal functions, such as cell migration, neurite outgrowth, and synaptic plasticity.
Topics: Actin Cytoskeleton; Actins; Amyloid beta-Protein Precursor; Animals; Humans; Models, Biological; Nerve Tissue Proteins; Protein Binding
PubMed: 34202290
DOI: 10.3390/cells10071599 -
Journal of Cell Science Nov 2023The crosstalk between the actin network and microtubules is essential for cell polarity. It orchestrates microtubule organization within the cell, driven by the...
The crosstalk between the actin network and microtubules is essential for cell polarity. It orchestrates microtubule organization within the cell, driven by the asymmetry of actin architecture along the cell periphery. The physical intertwining of these networks regulates spatial organization and force distribution in the microtubule network. Although their biochemical interactions are becoming clearer, the mechanical aspects remain less understood. To explore this mechanical interplay, we developed an in vitro reconstitution assay to investigate how dynamic microtubules interact with various actin filament structures. Our findings revealed that microtubules can align and move along linear actin filament bundles through polymerization force. However, they are unable to pass through when encountering dense branched actin meshworks, similar to those present in the lamellipodium along the periphery of the cell. Interestingly, immobilizing microtubules through crosslinking with actin or other means allow the buildup of pressure, enabling them to breach these dense actin barriers. This mechanism offers insights into microtubule progression towards the cell periphery, with them overcoming obstacles within the denser parts of the actin network and ultimately contributing to cell polarity establishment.
Topics: Actins; Microtubules; Actin Cytoskeleton; Cell Polarity; Pseudopodia
PubMed: 37870087
DOI: 10.1242/jcs.261667 -
Cytoskeleton (Hoboken, N.J.) 2024Mitochondria are the powerhouse of the cell and play important roles in multiple cellular processes including cell metabolism, proliferation, and programmed cell death.... (Review)
Review
Mitochondria are the powerhouse of the cell and play important roles in multiple cellular processes including cell metabolism, proliferation, and programmed cell death. Mitochondria are double-membrane organelles with the inner membrane folding inward to form cristae. Mitochondria networks undergo dynamic fission and fusion. Deregulation of mitochondrial structure has been linked to perturbed mitochondrial membrane potential and disrupted metabolism, as evidenced in tumorigenesis, neurodegenerative diseases, etc. Actin and its motors-myosins have long been known to generate mechanical forces and participate in short-distance cargo transport. Accumulating knowledge from biochemistry and live cell/electron microscope imaging has demonstrated the role of actin filaments in pre-constricting the mitochondria during fission. Recent studies have suggested the involvement of myosins in cristae maintenance and mitochondria quality control. Here, we review current findings and discuss future directions in the emerging fields of cytoskeletal regulation in cristae formation, mitochondrial dynamics, intracellular transport, and mitocytosis, with focus on the actin cytoskeleton and its motor proteins.
Topics: Actin Cytoskeleton; Mitochondria; Humans; Animals; Mitochondrial Dynamics; Actins
PubMed: 37929797
DOI: 10.1002/cm.21804 -
Journal of Biochemistry Feb 2024Blebs are membrane structures formed by the detachment of the plasma membrane from the underlying actin cytoskeleton. It is now clear that a wide variety of cells,... (Review)
Review
Blebs are membrane structures formed by the detachment of the plasma membrane from the underlying actin cytoskeleton. It is now clear that a wide variety of cells, including cancer cells, actively form blebs for cell migration and cell survival. The expansion of blebs has been regarded as the passive ballooning of the plasma membrane by an abrupt increase in intracellular pressure. However, recent studies revealed the importance of 'cytoplasmic zoning', i.e. local changes in the hydrodynamic properties and the ionic and protein content of the cytoplasm. In this review, we summarize the current understanding of the molecular mechanisms behind cytoplasmic zoning and its role in bleb expansion.
Topics: Cytoplasm; Cytosol; Cell Membrane; Actin Cytoskeleton; Actins
PubMed: 37943501
DOI: 10.1093/jb/mvad084 -
European Journal of Cell Biology Jun 2024At the cell surface, the actin cytoskeleton and the plasma membrane interact reciprocally in a variety of processes related to the remodeling of the cell surface. The... (Review)
Review
At the cell surface, the actin cytoskeleton and the plasma membrane interact reciprocally in a variety of processes related to the remodeling of the cell surface. The actin cytoskeleton has been known to modulate membrane organization and reshape the membrane. To this end, actin-membrane linking molecules play a major role in regulating actin assembly and spatially direct the interaction between the actin cytoskeleton and the membrane. While studies in cells have provided a wealth of knowledge on the molecular composition and interactions of the actin-membrane interface, the complex molecular interactions make it challenging to elucidate the precise actions of the actin-membrane linkers at the interface. Synthetic reconstituted systems, consisting of model membranes and purified proteins, have been a powerful approach to elucidate how actin-membrane linkers direct actin assembly to drive membrane shape changes. In this review, we will focus only on several actin-membrane linkers that have been studied by using reconstitution systems. We will discuss the design principles of these reconstitution systems and how they have contributed to the understanding of the cellular functions of actin-membrane linkers. Finally, we will provide a perspective on future research directions in understanding the intricate actin-membrane interaction.
Topics: Cell Membrane; Actins; Humans; Animals; Actin Cytoskeleton
PubMed: 38461706
DOI: 10.1016/j.ejcb.2024.151402 -
Brain Research Bulletin Jan 2023Directed outgrowth of axons is fundamental for the establishment of neuronal networks. Axon outgrowth is guided by growth cones, highly motile structures enriched in... (Review)
Review
Directed outgrowth of axons is fundamental for the establishment of neuronal networks. Axon outgrowth is guided by growth cones, highly motile structures enriched in filamentous actin (F-actin) located at the axons' distal tips. Growth cones exploit F-actin-based protrusions to scan the environment for guidance cues, and they contain the sensory apparatus to translate guidance cue information into intracellular signaling cascades. These cascades act upstream of actin-binding proteins (ABP) and thereby control assembly and disassembly of F-actin. Spatiotemporally controlled F-actin dis-/assembly in growth cones steers the axon towards attractants and away from repellents, and it thereby navigates the axon through the developing nervous system. Hence, ABP that control F-actin dynamics emerged as critical regulators of neuronal network formation. In the present review article, we will summarize and discuss current knowledge of the mechanisms that control remodeling of the actin cytoskeleton in growth cones, focusing on recent progress in the field. Further, we will introduce tools and techniques that allow to study actin regulatory mechanism in growth cones.
Topics: Growth Cones; Actins; Actin Cytoskeleton; Axons; Microfilament Proteins
PubMed: 36336143
DOI: 10.1016/j.brainresbull.2022.10.019 -
Trends in Biochemical Sciences May 2023Actin, one of the most abundant proteins in nature and a key component of the cytoskeleton, undergoes a unique multistep N-terminal (Nt) maturation. In a recent report,...
Actin, one of the most abundant proteins in nature and a key component of the cytoskeleton, undergoes a unique multistep N-terminal (Nt) maturation. In a recent report, Haahr et al. identified actin maturation protease (ACTMAP) as the dedicated actin aminopeptidase and showed that its absence is associated with abnormal muscle physiology.
Topics: Actins; Cytoskeleton; Actin Cytoskeleton
PubMed: 36804256
DOI: 10.1016/j.tibs.2023.02.002