scholarly journals The structure of the actin filament uncapping complex mediated by twinfilin

2021 ◽  
Vol 7 (5) ◽  
pp. eabd5271
Author(s):  
Dennis M. Mwangangi ◽  
Edward Manser ◽  
Robert C. Robinson
Keyword(s):  
Actin Filament ◽  
Protein Interactions ◽  
Protein Complex ◽  
Actin Filaments ◽  
Actin Binding ◽  
Capping Protein ◽  
Binding Surface ◽  
Actin Capping Protein ◽  
Actin Capping

Uncapping of actin filaments is essential for driving polymerization and depolymerization dynamics from capping protein–associated filaments; however, the mechanisms of uncapping leading to rapid disassembly are unknown. Here, we elucidated the x-ray crystal structure of the actin/twinfilin/capping protein complex to address the mechanisms of twinfilin uncapping of actin filaments. The twinfilin/capping protein complex binds to two G-actin subunits in an orientation that resembles the actin filament barbed end. This suggests an unanticipated mechanism by which twinfilin disrupts the stable capping of actin filaments by inducing a G-actin conformation in the two terminal actin subunits. Furthermore, twinfilin disorders critical actin-capping protein interactions, which will assist in the dissociation of capping protein, and may promote filament uncapping through a second mechanism involving V-1 competition for an actin-binding surface on capping protein. The extensive interactions with capping protein indicate that the evolutionary conserved role of twinfilin is to uncap actin filaments.

scholarly journals Capping protein regulates actin dynamics during cytokinetic midbody maturation

2018 ◽  
Vol 115 (9) ◽  
pp. 2138-2143 ◽  
Author(s):  
Stephen J. Terry ◽  
Federico Donà ◽  
Paul Osenberg ◽  
Jeremy G. Carlton ◽  
Ulrike S. Eggert
Keyword(s):  
Actin Filaments ◽  
Actin Polymerization ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Capping Protein ◽  
Cytoskeletal Remodeling ◽  
Daughter Cells ◽  
Actin Capping Protein ◽  
Activity Loss ◽  
Actin Capping

During cytokinesis, a cleavage furrow generated by actomyosin ring contraction is restructured into the midbody, a platform for the assembly of the abscission machinery that controls the final separation of daughter cells. The polymerization state of F-actin is important during assembly, ingression, disassembly, and closure of the contractile ring and for the cytoskeletal remodeling that accompanies midbody formation and progression to abscission. Actin filaments must be cleared from the abscission sites before the final cut can take place. Although many conserved proteins interact with and influence the polymerization state of actin filaments, it is poorly understood how they regulate cytokinesis in higher eukaryotes. We report here that the actin capping protein (CP), a barbed end actin binding protein, participates in the control of actin polymerization during later stages of cytokinesis in human cells. Cells depleted of CP furrow and form early midbodies, but they fail cytokinesis. Appropriate recruitment of the ESCRT-III abscission machinery to the midbody is impaired, preventing the cell from progressing to the abscission stage. To generate actin filaments of optimal length, different actin nucleators, such as formins, balance CP’s activity. Loss of actin capping activity leads to excessive accumulation of formin-based linear actin filaments. Depletion of the formin FHOD1 results in partial rescue of CP-induced cytokinesis failure, suggesting that it can antagonize CP activity during midbody maturation. Our work suggests that the actin cytoskeleton is remodeled in a stepwise manner during cytokinesis, with different regulators at different stages required for successful progression to abscission.

scholarly journals GJA1-20k, an internally translated isoform of Connexin 43, is an actin capping protein

2022 ◽  
Author(s):  
Robin Mark Shaw ◽  
Rachel Baum ◽  
Joseph Alexander Palatinus ◽  
Miriam Waghalter ◽  
Daisuke Shimura ◽  
...  
Keyword(s):  
Actin Filaments ◽  
Connexin 43 ◽  
Ischemia Reperfusion ◽  
Mitochondrial Fission ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Binding Motif ◽  
Capping Protein ◽  
Actin Capping Protein ◽  
Actin Capping

Previously, we identified that GJA1-20k, an internally translated isoform of Connexin 43, mediates an actin-dependent protective form of mitochondrial fission (Shimura, Nuebel et al. 2021). We found that when GJA1-20k is present, bands of actin surround mitochondria at locations enriched with GJA1-20k, inducing mitochondrial fission which generates less oxygen free radicals, protecting hearts subjected to ischemia-reperfusion injury. Here, we report that GJA1-20k is a direct actin binding protein and thereby identify the mechanism by which GJA1-20k is able to recruit and stabilize actin filaments around the mitochondria. Surprisingly, GJA1-20k functions as a canonical actin capping protein, producing both truncated actin puncta and stabilized actin filaments. GJA1-20k contains an RPEL-like actin binding motif, and we confirm with both computational modeling and biochemistry, that this domain is crucial for actin capping. The actin capping functionality of GJA1-20k adds GJA1-20k to the family of proteins that regulate actin dynamics. As a stress responsive protein, GJA1-20k can help explain cytoskeletal dependent responses to cellular stress, from delivery of channels to affecting mitochondrial size and function.

scholarly journals CapZ integrates several signaling pathways in response to mechanical stiffness

2019 ◽  
Vol 151 (5) ◽  
pp. 660-669 ◽  
Author(s):  
Christopher Solís ◽  
Brenda Russell
Keyword(s):  
Mechanical Load ◽  
Phosphorylation Site ◽  
Tight Binding ◽  
Neonatal Rat ◽  
Actin Binding ◽  
Mechanical Stimuli ◽  
Muscle Adaptation ◽  
Capping Protein ◽  
Actin Capping Protein ◽  
Actin Capping

Muscle adaptation is a response to physiological demand elicited by changes in mechanical load, hormones, or metabolic stress. Cytoskeletal remodeling processes in many cell types are thought to be primarily regulated by thin filament formation due to actin-binding accessory proteins, such as the actin-capping protein. Here, we hypothesize that in muscle, the actin-capping protein (named CapZ) integrates signaling by a variety of pathways, including phosphorylation and phosphatidylinositol 4,5-bisphosphate (PIP2) binding, to regulate muscle fiber growth in response to mechanical load. To test this hypothesis, we assess mechanotransduction signaling that regulates muscle growth using neonatal rat ventricular myocytes cultured on substrates with the stiffness of the healthy myocardium (10 kPa), fibrotic myocardium (100 kPa), or glass. We investigate how PIP2 signaling affects CapZ using the PIP2 sequestering agent neomycin and the effect of PKC-mediated CapZ phosphorylation using the PKC-activating drug phorbol 12-myristate 13-acetate (PMA). Molecular simulations suggest that close interactions between PIP2 and the β-tentacle of CapZ are modified by phosphorylation at T267. Fluorescence recovery after photobleaching (FRAP) demonstrates that the kinetic binding constant of CapZ to sarcomeric thin filaments in living muscle cells increases with stiffness or PMA treatment but is diminished by PIP2 reduction. Furthermore, CapZ with a deletion of the β-tentacle that lacks the phosphorylation site T267 shows increased FRAP kinetics with lack of sensitivity to PMA treatment or PIP2 reduction. Förster resonance energy transfer (FRET) probes the molecular interactions between PIP2 and CapZ, which are decreased by PIP2 availability or by the β-tentacle truncation. These data suggest that CapZ is bound to actin tightly in the idle, locked state, with little phosphorylation or PIP2 binding. However, this tight binding is loosened in growth states triggered by mechanical stimuli such as substrate stiffness, which may have relevance to fibrotic heart disease.

scholarly journals Dynamics of Tpm1.8 domains on actin filaments with single molecule resolution

2020 ◽  
Author(s):  
Ilina Bareja ◽  
Hugo Wioland ◽  
Miro Janco ◽  
Philip R. Nicovich ◽  
Antoine Jégou ◽  
...  
Keyword(s):  
Actin Filament ◽  
Single Molecule ◽  
Actin Filaments ◽  
High Probability ◽  
Actin Binding ◽  
Single Molecule Level ◽  
Filament Dynamics ◽  
Kinetics Of ◽  
Insight Into

ABSTRACTTropomyosins regulate dynamics and functions of the actin cytoskeleton by forming long chains along the two strands of actin filaments that act as gatekeepers for the binding of other actin-binding proteins. The fundamental molecular interactions underlying the binding of tropomyosin to actin are still poorly understood. Using microfluidics and fluorescence microscopy, we observed the binding of fluorescently labelled tropomyosin isoform Tpm1.8 to unlabelled actin filaments in real time. This approach in conjunction with mathematical modeling enabled us to quantify the nucleation, assembly and disassembly kinetics of Tpm1.8 on single filaments and at the single molecule level. Our analysis suggests that Tpm1.8 decorates the two strands of the actin filament independently. Nucleation of a growing tropomyosin domain proceeds with high probability as soon as the first Tpm1.8 molecule is stabilised by the addition of a second molecule, ultimately leading to full decoration of the actin filament. In addition, Tpm1.8 domains are asymmetrical, with enhanced dynamics at the edge oriented towards the barbed end of the actin filament. The complete description of Tpm1.8 kinetics on actin filaments presented here provides molecular insight into actin-tropomyosin filament formation and the role of tropomyosins in regulating actin filament dynamics.

scholarly journals An Essential Role for the Interaction Between Hyaluronan and Hyaluronan Binding Proteins During Joint Development

1998 ◽  
Vol 46 (5) ◽  
pp. 641-651 ◽  
Author(s):  
Gary P. Dowthwaite ◽  
Jo C. W. Edwards ◽  
Andrew A. Pitsillides
Keyword(s):  
Actin Filament ◽  
Binding Proteins ◽  
Joint Line ◽  
Joint Formation ◽  
Capping Protein ◽  
Initial Separation ◽  
Actin Capping Protein ◽  
Filament Bundles ◽  
Actin Capping ◽  
Hyaluronan Binding

We studied the expression of hyaluronan binding proteins (HABPs) during the development of embryonic chick joints, using immunocytochemistry and biotinylated HA. The expression of actin capping proteins and of actin itself was also studied because the cytoskeleton is important in controlling HA-HABP interactions. Three cell surface HABPs were localized in the epiphyseal cartilage, articular fibrocartilage, and interzone that comprise the developing joint. Of these three HABPs, CD44 was associated with the articular fibrocartilages and interzone, whereas RHAMM and the IVd4 epitope were associated with all three tissues. Biotinylated HA was localized to interzone and articular fibrocartilages before cavity formation and within epiphyseal chondrocytes post cavitation. Actin filament bundles were observed at the developing joint line, as was the expression of the actin capping protein moesin. Manipulation of joint cavity development, using oligosaccharides of HA, disrupted joint formation and was associated with decreases in CD44 and actin filament expression as well as decreased hyaluronan synthetic capability. These results suggest that HA is actively bound by CD44 at the developing joint line and that HA-HABP interactions play a major role in the initial separation events occurring during joint formation.

scholarly journals The actin-capping protein alpha-adducin is required for T-cell costimulation

2019 ◽  
Author(s):  
Timothy J. Thauland ◽  
Manish J. Butte
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Conditional Knockout ◽  
Capping Protein ◽  
Actin Capping Protein ◽  
Actin Capping ◽  
Spectrin Network

AbstractAlpha-adducin (Add1) is a critical component of the actin-spectrin network in erythrocytes, acting to cap the fast-growing, barbed ends of actin filaments, and recruiting spectrin to these junctions. Add1 is highly expressed in T cells, but its role in T-cell activation has not been examined. Using a conditional knockout model, we show that Add1 is necessary for complete activation of CD4+ T cells in response to low levels of antigen but is dispensable for CD8+ T cell activation and response to infection. Surprisingly, costimulatory signals through CD28 were completely abrogated in the absence of Add1. This study is the first to examine the role of actin-capping in T cells, and it reveals a previously unappreciated role for the actin cytoskeleton in regulating costimulation.

scholarly journals Ezrin has a COOH-terminal actin-binding site that is conserved in the ezrin protein family.

1994 ◽  
Vol 126 (6) ◽  
pp. 1445-1453 ◽  
Author(s):  
O Turunen ◽  
T Wahlström ◽  
A Vaheri
Keyword(s):  
Binding Site ◽  
Protein Family ◽  
Actin Binding ◽  
Capping Protein ◽  
Terminal Domain ◽  
Membrane Cytoskeleton ◽  
Actin Capping Protein ◽  
Binding Capability ◽  
Actin Capping ◽  
Actin Binding Site

Ezrin, previously also known as cytovillin, p81, and 80K, is a cytoplasmic protein enriched in microvilli and other cell surface structures. Ezrin is postulated to have a membrane-cytoskeleton linker role. Recent findings have also revealed that the NH2-terminal domain of ezrin is associated with the plasma membrane and the COOH-terminal domain with the cytoskeleton (Algrain, M., O. Turunen, A. Vaheri, D. Louvard, and M. Arpin. 1993. J. Cell Biol. 120: 129-139). Using bacterially expressed fragments of ezrin we now demonstrate that ezrin has an actin-binding capability. We used glutathione-S-transferase fusion proteins of truncated ezrin in affinity chromatography to bind actin from the cell extract or purified rabbit muscle actin. We detected a binding site for filamentous actin that was localized to the COOH-terminal 34 amino acids of ezrin. No binding of monomeric actin was detected in the assay. The region corresponding to the COOH-terminal actin-binding site in ezrin is highly conserved in moesin, actin-capping protein radixin and EM10 protein of E. multilocularis, but not in merlin/schwannomin. Consequently, this site is a potential actin-binding site also in the other members of the protein family. Furthermore, the actin-binding site in ezrin shows sequence homology to the actin-binding site in the COOH terminus of the beta subunit of the actin-capping protein CapZ and one of the potential actin-binding sites in myosin heavy chain. The actin-binding capability of ezrin supports its proposed role as a membrane-cytoskeleton linker.

scholarly journals Regulation of Sodium Channel Activity by Capping of Actin Filaments

2003 ◽  
Vol 14 (4) ◽  
pp. 1709-1716 ◽  
Author(s):  
Ekaterina V. Shumilina ◽  
Yuri A. Negulyaev ◽  
Elena A. Morachevskaya ◽  
Horst Hinssen ◽  
Sofia Yu Khaitlina
Keyword(s):  
Plasma Membrane ◽  
Sodium Channel ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Actin Dynamics ◽  
Channel Activity ◽  
Capping Protein ◽  
Channel Inactivation ◽  
Actin Capping Protein ◽  
Actin Capping

Ion transport in various tissues can be regulated by the cortical actin cytoskeleton. Specifically, involvement of actin dynamics in the regulation of nonvoltage-gated sodium channels has been shown. Herein, inside-out patch clamp experiments were performed to study the effect of the heterodimeric actin capping protein CapZ on sodium channel regulation in leukemia K562 cells. The channels were activated by cytochalasin-induced disruption of actin filaments and inactivated by G-actin under ionic conditions promoting rapid actin polymerization. CapZ had no direct effect on channel activity. However, being added together with G-actin, CapZ prevented actin-induced channel inactivation, and this effect occurred at CapZ/actin molar ratios from 1:5 to 1:100. When actin was allowed to polymerize at the plasma membrane to induce partial channel inactivation, subsequent addition of CapZ restored the channel activity. These results can be explained by CapZ-induced inhibition of further assembly of actin filaments at the plasma membrane due to the modification of actin dynamics by CapZ. No effect on the channel activity was observed in response to F-actin, confirming that the mechanism of channel inactivation does not involve interaction of the channel with preformed filaments. Our data show that actin-capping protein can participate in the cytoskeleton-associated regulation of sodium transport in nonexcitable cells.

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