Reorganization and turnover of actin filament architectures in cell

Sheterline, Peter; Handel, Susan H.; Hendry, K. A. K.

doi:10.1042/bst0191120

Cited by 33 publications

(47 citation statements)

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“…In all simulations of F-MreB initialized from the MreB crystal structure, MreB subunits equilibrated to a closed state, suggesting that the adsorbed subunit would close in an extended simulation. ) is required for the in vitro polymerization of MreB (1,12,(15)(16)(17) and actin (11) and has been hypothesized to stabilize the bound nucleotide (27). To determine the effects of Mg 2+ on the structural dynamics of MreB monomers, we performed simulations of MreB as a monomer or dimer bound to ATP with the chelating Mg 2+ ion removed ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…However, MreB and actin share only 15% residue identity, mostly between conserved ATPase motifs common to the actin superfamily (10). Although both actin and MreB regulate cell shape, actin forms dynamic, branched cytosolic networks (11), whereas MreB forms distinct, stable filaments in vitro (12) and associates with the membrane in vivo to coordinate cell-wall elongation in many rod-shaped bacteria (13). Thus, the validity of inferring MreB filament properties from the extensive structural knowledge of actin is unclear.…”

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confidence: 99%

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Effects of polymerization and nucleotide identity on the conformational dynamics of the bacterial actin homolog MreB

Colavin

Hsin²,

Huang

2014

Proc. Natl. Acad. Sci. U.S.A.

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The assembly of protein filaments drives many cellular processes, from nucleoid segregation, growth, and division in single cells to muscle contraction in animals. In eukaryotes, shape and motility are regulated through cycles of polymerization and depolymerization of actin cytoskeletal networks. In bacteria, the actin homolog MreB forms filaments that coordinate the cell-wall synthesis machinery to regulate rod-shaped growth and contribute to cellular stiffness through unknown mechanisms. Like actin, MreB is an ATPase and requires ATP to polymerize, and polymerization promotes nucleotide hydrolysis. However, it is unclear whether other similarities exist between MreB and actin because the two proteins share low sequence identity and have distinct cellular roles. Here, we use all-atom molecular dynamics simulations to reveal surprising parallels between MreB and actin structural dynamics. We observe that MreB exhibits actin-like polymerization-dependent structural changes, wherein polymerization induces flattening of MreB subunits, which restructures the nucleotide-binding pocket to favor hydrolysis. MreB filaments exhibited nucleotide-dependent intersubunit bending, with hydrolyzed polymers favoring a straighter conformation. We use steered simulations to demonstrate a coupling between intersubunit bending and the degree of flattening of each subunit, suggesting cooperative bending along a filament. Taken together, our results provide molecular-scale insight into the diversity of structural states of MreB and the relationships among polymerization, hydrolysis, and filament properties, which may be applicable to other members of the broad actin family.bacterial cytoskeleton | polymer mechanics | actin superfamily | filament assembly | cell shape control

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Effects of polymerization and nucleotide identity on the conformational dynamics of the bacterial actin homolog MreB

Colavin

Hsin²,

Huang

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…In the presence of Mg 21 -ions, the dissociation constant for the (1)-end of the filament is about 0.1 mm and that of the (±)-end 0.7 mm (reviewed in [29]). Thus, between 0.1 and 0.7 mm growth of actin filaments takes place at the (1)-end.…”

Section: Polymerization and Atpase Activity Of Wild-type And Mutant Amentioning

confidence: 99%

Mutational analysis of arginine 177 in the nucleotide binding site of beta-actin

et al. 2000

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Actin ADP-ribosylated at arginine 177 is unable to hydrolyze ATP, and the R177 side chain is in a position similar to that of the catalytically essential lysine 71 in heat shock cognate protein Hsc70, another member of the actin-fold family of proteins. Therefore, actin residue R177 has been implicated in the mechanism of ATP hydrolysis. This paper compares wild-type b-actin with a mutant in which R177 has been replaced by aspartic acid. The mutant b-actin was expressed in Saccharomyces cerevisiae and purified by DNase I-affinity chromatography. The mutant protein exhibited a reduced thermal stability and an increased nucleotide exchange rate, suggesting a weakened interdomain connection. The ATPase activity of G-actin and the ATPase activity expressed during polymerization were unaffected by the R177D replacement, showing that this residue is not involved in catalysis. In the presence of polymerizing salts, ATP hydrolysis by both wild-type Mg-b-actin and the mutant protein preceded filament formation. With the mutant actin, the initial rate of ATP hydrolysis was as high as with wild-type actin, but polymer formation was slower, reached lower steady-state levels, and the polymers formed exhibited much lower viscosity. The critical concentration of polymerization (A cc ) of the mutant actin was increased 10-fold as compared to wild-type actin. Filaments formed from the R177D mutant b-actin bound phalloidin.

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“…An apparent K d value was calculated by measuring the shift in the steady state critical concentration ( C c ) for pollen actin assembly in the presence of profilin. The C c is the minimum G-actin concentration at which polymerization will occur (Sheterline et al, 1998) Table 3. The values for ZmPRO5 and ZmPRO4 were significantly (P Ͻ 0.001) lower than those for ZmPRO1.…”

Section: Zmpro5 and Endosperm Profilin Inhibit Actin Polymerization Bmentioning

confidence: 99%

Maize Profilin Isoforms Are Functionally Distinct

2000

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Profilin is an actin monomer binding protein that, depending on the conditions, causes either polymerization or depolymerization of actin filaments. In plants, profilins are encoded by multigene families. In this study, an analysis of native and recombinant proteins from maize demonstrates the existence of two classes of functionally distinct profilin isoforms. Class II profilins, including native endosperm profilin and a new recombinant protein, ZmPRO5, have biochemical properties that differ from those of class I profilins. Class II profilins had higher affinity for poly-L -proline and sequestered more monomeric actin than did class I profilins. Conversely, a class I profilin inhibited hydrolysis of membrane phosphatidylinositol-4,5-bisphosphate by phospholipase C more strongly than did a class II profilin. These biochemical properties correlated with the ability of class II profilins to disrupt actin cytoplasmic architecture in live cells more rapidly than did class I profilins. The actin-sequestering activity of both maize profilin classes was found to be dependent on the concentration of free calcium. We propose a model in which profilin alters cellular concentrations of actin polymers in response to fluctuations in cytosolic calcium concentration. These results provide strong evidence that the maize profilin gene family consists of at least two classes, with distinct biochemical and live-cell properties, implying that the maize profilin isoforms perform distinct functions in the plant. INTRODUCTIONPlant cells often respond to intracellular and extracellular cues by reorganizing their microtubule and actin microfilament cytoskeletons. Actin reorganization in particular is necessary for or coincident with a variety of environmentally influenced processes, including cell division, cell elongation, responses to wounding or pathogen attack, plastid positioning, and pollen germination and extension of the pollen tube (reviewed in Taylor and Hepler, 1997;Nick, 1999;Staiger, 2000). In all eukaryotic cells, actin reorganization is thought to be controlled by actin binding proteins that regulate the spatial and temporal polymerization and depolymerization of actin monomers (globular or G-actin) into filamentous actin (F-actin) and that also organize the cytoskeleton into macromolecular structures. Actin binding proteins can be placed into several broad groups, based on their functional characteristics in vitro. Many are sensitive to changes in calcium and pH, and some are thought to be regulated through signal transduction pathways by interacting with polyphosphoinositides or to act as downstream effectors of small G proteins (Schmidt and Hall, 1998).Profilins are low molecular mass (12 to 15 kD), abundant, cytosolic actin monomer binding proteins that form a 1:1 complex with G-actin. In addition to actin, profilins also interact with poly-L -proline (PLP) and proline-rich proteins, membrane polyphosphoinositides, phosphatidylinositol-3-kinase, annexin, and several multiprotein complexes that are implicated in the ...

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Reorganization and turnover of actin filament architectures in cell

Cited by 33 publications

References 3 publications

Effects of polymerization and nucleotide identity on the conformational dynamics of the bacterial actin homolog MreB

Effects of polymerization and nucleotide identity on the conformational dynamics of the bacterial actin homolog MreB

Mutational analysis of arginine 177 in the nucleotide binding site of beta-actin

Maize Profilin Isoforms Are Functionally Distinct

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