scholarly journals Myopathy-Sensitive G-Actin Segment 227-235 Is Involved in Salt-Induced Stabilization of Contacts within the Actin Filament

2021 ◽  
Vol 22 (5) ◽  
pp. 2327
Author(s):  
Joanna Gruszczynska-Biegala ◽  
Andrzej Stefan ◽  
Andrzej A. Kasprzak ◽  
Piotr Dobryszycki ◽  
Sofia Khaitlina ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Actin Filament ◽  
Actin Filaments ◽  
Dynamic Properties ◽  
Cation Binding ◽  
Subunit Exchange ◽  
High Affinity ◽  
Cation Binding Site ◽  
D Loop ◽  
Α Helix

Formation of stable actin filaments, critically important for actin functions, is determined by the ionic strength of the solution. However, not much is known about the elements of the actin fold involved in ionic-strength-dependent filament stabilization. In this work, F-actin was destabilized by Cu2+ binding to Cys374, and the effects of solvent conditions on the dynamic properties of F-actin were correlated with the involvement of Segment 227-235 in filament stabilization. The results of our work show that the presence of Mg2+ at the high-affinity cation binding site of Cu-modified actin polymerized with MgCl2 strongly enhances the rate of filament subunit exchange and promotes the filament instability. In the presence of 0.1 M KCl, the filament subunit exchange was 2–3-fold lower than that in the MgCl2-polymerized F-actin. This effect correlates with the reduced accessibility of the D-loop and Segment 227-235 on opposite filament strands, consistent with an ionic-strength-dependent conformational change that modulates involvement of Segment 227-235 in stabilization of the intermonomer interface. KCl may restrict the mobility of the α-helix encompassing part of Segment 227-235 and/or be bound to Asp236 at the boundary of Segment 227-235. These results provide experimental evidence for the involvement of Segment 227-235 in salt-induced stabilization of contacts within the actin filament and suggest that they can be weakened by mutations characteristic of actin-associated myopathies.

scholarly journals A Correlative Analysis of Actin Filament Assembly, Structure, and Dynamics

1997 ◽  
Vol 138 (3) ◽  
pp. 559-574 ◽  
Author(s):  
Michel O. Steinmetz ◽  
Kenneth N. Goldie ◽  
Ueli Aebi
Keyword(s):  
Actin Filament ◽  
Divalent Cation ◽  
Actin Filaments ◽  
Metal Ion ◽  
Cation Binding ◽  
Polymerization Reaction ◽  
Structure And Dynamics ◽  
Filament Assembly ◽  
Cation Binding Site ◽  
Assembly Structure

The effect of the type of metal ion (i.e., Ca2+, Mg2+, or none) bound to the high-affinity divalent cation binding site (HAS) of actin on filament assembly, structure, and dynamics was investigated in the absence and presence of the mushroom toxin phalloidin. In agreement with earlier reports, we found the polymerization reaction of G-actin into F-actin filaments to be tightly controlled by the type of divalent cation residing in its HAS. Moreover, novel polymerization data are presented indicating that LD, a dimer unproductive by itself, does incorporate into growing F-actin filaments. This observation suggests that during actin filament formation, in addition to the obligatory nucleation– condensation pathway involving UD, a productive filament dimer, a facultative, LD-based pathway is implicated whose abundance strongly depends on the exact polymerization conditions chosen. The “ragged” and “branched” filaments observed during the early stages of assembly represent a hallmark of LD incorporation and might be key to producing an actin meshwork capable of rapidly assembling and disassembling in highly motile cells. Hence, LD incorporation into growing actin filaments might provide an additional level of regulation of actin cytoskeleton dynamics. Regarding the structure and mechanical properties of the F-actin filament at steady state, no significant correlation with the divalent cation residing in its HAS was found. However, compared to native filaments, phalloidin-stabilized filaments were stiffer and yielded subtle but significant structural changes. Together, our data indicate that whereas the G-actin conformation is tightly controlled by the divalent cation in its HAS, the F-actin conformation appears more robust than this variation. Hence, we conclude that the structure and dynamics of the Mg–F-actin moiety within the thin filament are not significantly modulated by the cyclic Ca2+ release as it occurs in muscle contraction to regulate the actomyosin interaction via troponin.

scholarly journals Experimental and Theoretical Characterization of the High-Affinity Cation-Binding Site of the Purple Membrane

1998 ◽  
Vol 75 (2) ◽  
pp. 777-784 ◽  
Author(s):  
Leonardo Pardo ◽  
Francesc Sepulcre ◽  
Josep Cladera ◽  
Mireia Duñach ◽  
Amílcar Labarta ◽  
...  
Keyword(s):  
Binding Site ◽  
Purple Membrane ◽  
Cation Binding ◽  
High Affinity ◽  
Cation Binding Site ◽  
Theoretical Characterization

scholarly journals An extended x-ray absorption fine structure study of the high-affinity cation-binding site in the purple membrane

1996 ◽  
Vol 70 (2) ◽  
pp. 852-856 ◽  
Author(s):  
F. Sepulcre ◽  
J. Cladera ◽  
J. García ◽  
M.G. Proietti ◽  
J. Torres ◽  
...  
Keyword(s):  
Fine Structure ◽  
Binding Site ◽  
Structure Study ◽  
Purple Membrane ◽  
Cation Binding ◽  
X Ray ◽  
High Affinity ◽  
Absorption Fine ◽  
Cation Binding Site ◽  
X Ray Absorption

scholarly journals Unusual dynamics of the divergent malaria parasite PfAct1 actin filament

2019 ◽  
Vol 116 (41) ◽  
pp. 20418-20427 ◽  
Author(s):  
Hailong Lu ◽  
Patricia M. Fagnant ◽  
Kathleen M. Trybus
Keyword(s):  
Actin Filament ◽  
Dynamic Properties ◽  
Critical Concentration ◽  
Gliding Motility ◽  
Macromolecular Complex ◽  
Fast Kinetics ◽  
Membrane Complex ◽  
D Loop ◽  
Order Of Magnitude ◽  
Inner Membrane Complex

Gliding motility and host cell invasion by the apicomplexan parasite Plasmodium falciparum (Pf), the causative agent of malaria, is powered by a macromolecular complex called the glideosome that lies between the parasite plasma membrane and the inner membrane complex. The glideosome core consists of a single-headed class XIV myosin PfMyoA and a divergent actin PfAct1. Here we use total internal reflection fluorescence microscopy to visualize growth of individual unstabilized PfAct1 filaments as a function of time, an approach not previously used with this actin isoform. Although PfAct1 was thought to be incapable of forming long filaments, filaments grew as long as 30 µm. Polymerization occurs via a nucleation–elongation mechanism, but with an ∼4 µM critical concentration, an order-of-magnitude higher than for skeletal actin. Protomers disassembled from both the barbed and pointed ends of the actin filament with similar fast kinetics of 10 to 15 subunits/s. Rapid treadmilling, where the barbed end of the filament grows and the pointed end shrinks while maintaining an approximately constant filament length, was visualized near the critical concentration. Once ATP has been hydrolyzed to ADP, the filament becomes very unstable, resulting in total dissolution in <40 min. Dynamics at the filament ends are suppressed in the presence of inorganic phosphate or more efficiently by BeFX. A chimeric PfAct1 with a mammalian actin D-loop forms a more stable filament. These unusual dynamic properties distinguish PfAct1 from more canonical actins, and likely contribute to the difficultly in visualizing PfAct1 filaments in the parasite.

Factors affecting movement of F-actin filaments propelled by skeletal muscle heavy meromyosin

1992 ◽  
Vol 262 (3) ◽  
pp. C714-C723 ◽  
Author(s):  
E. Homsher ◽  
F. Wang ◽  
J. R. Sellers
Keyword(s):  
Skeletal Muscle ◽  
Ionic Strength ◽  
Actin Filament ◽  
Molecular Motors ◽  
Actin Filaments ◽  
Heavy Meromyosin ◽  
Shortening Velocity ◽  
Weakly Bound ◽  
Factors Affecting ◽  
Cross Bridges

The measurement of fluorescent-labeled actin filament movement driven by mechanoenzymes (e.g., myosin) is an important methodology for the study of molecular motors. It is assumed that the filament velocity (Vf) is analogous to the unloaded shortening velocity (Vu) seen in muscle fibers. Methods are described to reproducibly quantitate the movement of these filaments and to select uniformly moving filaments and specify their Vf. Use of these techniques allowed comparison of Vf to literature values for Vu with regard to [ATP], [ADP], [Pi], pH, ionic strength (10-150 mM), and temperature (15-30 degrees C). Vf and Vu are quantitatively similar with respect to the effects of substrate and product concentrations and temperatures greater than 20 degrees C. However, Vf is more sensitive to decreases in pH and temperatures less than 20 degrees C than Vu. At ionic strengths of 50-150 mM, Vf and Vu exhibit similar ionic strength dependencies (decreasing with ionic strength). At ionic strengths less than 50 mM, Vf is markedly reduced. Results of experiments using adenosine 5'-O-(3-thiotriphosphate) suggest that increasing the number of weakly bound cross bridges does not seriously affect Vf. Thus, although Vf is a good analogue for Vu under certain conditions (elevated ionic strength and temperatures greater than 20 degrees C), under others it is not. The results of motility assays must be cautiously interpreted.

scholarly journals Structures and characterization of digoxin- and bufalin-bound Na+,K+-ATPase compared with the ouabain-bound complex

2015 ◽  
Vol 112 (6) ◽  
pp. 1755-1760 ◽  
Author(s):  
Mette Laursen ◽  
Jonas Lindholt Gregersen ◽  
Laure Yatime ◽  
Poul Nissen ◽  
Natalya U. Fedosova
Keyword(s):  
Binding Sites ◽  
Cation Binding ◽  
General Mechanism ◽  
Transmembrane Helices ◽  
Binding Properties ◽  
High Affinity ◽  
Cation Binding Site ◽  
Fine Tune ◽  
Specific Influence

Cardiotonic steroids (CTSs) are specific and potent inhibitors of the Na+,K+-ATPase, with highest affinity to the phosphoenzyme (E2P) forms. CTSs are comprised of a steroid core, which can be glycosylated, and a varying number of substituents, including a five- or six-membered lactone. These functionalities have specific influence on the binding properties. We report crystal structures of the Na+,K+-ATPase in the E2P form in complex with bufalin (a nonglycosylated CTS with a six-membered lactone) and digoxin (a trisaccharide-conjugated CTS with a five-membered lactone) and compare their characteristics and binding kinetics with the previously described E2P–ouabain complex to derive specific details and the general mechanism of CTS binding and inhibition. CTSs block the extracellular cation exchange pathway, and cation-binding sites I and II are differently occupied: A single Mg2+ is bound in site II of the digoxin and ouabain complexes, whereas both sites are occupied by K+ in the E2P–bufalin complex. In all complexes, αM4 adopts a wound form, characteristic for the E2P state and favorable for high-affinity CTS binding. We conclude that the occupants of the cation-binding site and the type of the lactone substituent determine the arrangement of αM4 and hypothesize that winding/unwinding of αM4 represents a trigger for high-affinity CTS binding. We find that the level of glycosylation affects the depth of CTS binding and that the steroid core substituents fine tune the configuration of transmembrane helices αM1–2.

scholarly journals Characterization of ruthenium red-binding sites of the Ca2+-ATPase from sarcoplasmic reticulum and their interaction with Ca2+-binding sites

1992 ◽  
Vol 287 (3) ◽  
pp. 767-774 ◽  
Author(s):  
S Corbalan-Garcia ◽  
J A Teruel ◽  
J C Gomez-Fernandez
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Sites ◽  
Ruthenium Red ◽  
Cation Binding ◽  
Binding Studies ◽  
High Affinity ◽  
Cation Binding Site ◽  
Kinetics Of ◽  
Fast Release

Sarcoplasmic reticulum Ca(2+)-ATPase has previously been shown to bind and dissociate two Ca2+ ions in a sequential mode. This behaviour is confirmed here by inducing sequential Ca2+ dissociation with Ruthenium Red. Ruthenium Red binds to sarcoplasmic reticulum vesicles (6 nmol/mg) with a Kd = 2 microM, producing biphasic kinetics of Ca2+ dissociation from the Ca(2+)-ATPase, decreasing the affinity for Ca2+ binding. Studies on the effect of Ca2+ on Ruthenium Red binding indicate that Ruthenium Red does not bind to the high-affinity Ca(2+)-binding sites, as suggested by the following observations: (i) micromolar concentrations of Ca2+ do not significantly alter Ruthenium Red binding to the sarcoplasmic reticulum; (ii) quenching of the fluorescence of fluorescein 5′-isothiocyanate (FITC) bound to Ca(2+)-ATPase by Ruthenium Red (resembling Ruthenium Red binding) is not prevented by micromolar concentrations of Ca2+; (iii) quenching of FITC fluorescence by Ca2+ binding to the high-affinity sites is achieved even though Ruthenium Red is bound to the Ca(2+)-ATPase; and (iv) micromolar Ca2+ concentrations prevent inhibition of the ATP-hydrolytic capability by dicyclohexylcarbodi-imide modification, but Ruthenium Red does not. However, micromolar concentrations of lanthanides (La3+ and Tb3+) and millimolar concentrations of bivalent cations (Ca2+ and Mg2+) inhibit Ruthenium Red binding as well as quenching of FITC-labelled Ca(2+)-ATPase fluorescence by Ruthenium Red. Studies of Ruthenium Red binding to tryptic fragments of Ca(2+)-ATPase, as demonstrated by ligand blotting, indicate that Ruthenium Red does not bind to the A1 subfragment. Our observations suggest that Ruthenium Red might bind to a cation-binding site in Ca(2+)-ATPase inducing fast release of the last bound Ca2+ by interactions between the sites.

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