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1.
Eur J Med Chem ; 247: 115008, 2023 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-36543032

RESUMO

Muscle myosin inhibition could be used to treat many medical conditions involving hypercontractile states, including muscle spasticity, chronic musculoskeletal pain, and hypertrophic cardiomyopathy. A series of 13 advanced analogs of 3-(N-butylethanimidoyl)ethyl)-4-hydroxy-2H-chromen-2-one (BHC) were synthesized to explore extended imine nitrogen side chains and compare aldimines vs. ketimines. None of the new analogs inhibit nonmuscle myosin in a cytokinesis assay. ATPase structure-activity relationships reveal that selectivity for cardiac vs. skeletal myosin can be tuned with subtle structural changes. None of the compounds inhibited smooth muscle myosin II. Docking the compounds to homology models of cardiac and skeletal myosin II gave rationales for the effects of side arm length on inhibition selectivity and for cardiac vs. skeletal myosin. Properties including solubility, stability and toxicity, suggest that certain BHC analogs may be useful as candidates for preclinical studies or as lead compounds for advanced candidates for drugs with cardiac or skeletal muscle myosin selectivity.


Assuntos
4-Hidroxicumarinas , Miosina Tipo II , Miosinas , Isoformas de Proteínas , Adenosina Trifosfatases
2.
J Gen Physiol ; 153(3)2021 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-33439241

RESUMO

Myosins in muscle assemble into filaments by interactions between the C-terminal light meromyosin (LMM) subdomains of the coiled-coil rod domain. The two head domains are connected to LMM by the subfragment-2 (S2) subdomain of the rod. Our mixed kinetic model predicts that the flexibility and length of S2 that can be pulled away from the filament affects the maximum distance working heads can move a filament unimpeded by actin-attached heads. It also suggests that it should be possible to observe a head remain stationary relative to the filament backbone while bound to actin (dwell), followed immediately by a measurable jump upon detachment to regain the backbone trajectory. We tested these predictions by observing filaments moving along actin at varying ATP using TIRF microscopy. We simultaneously tracked two different color quantum dots (QDs), one attached to a regulatory light chain on the lever arm and the other attached to an LMM in the filament backbone. We identified events (dwells followed by jumps) by comparing the trajectories of the QDs. The average dwell times were consistent with known kinetics of the actomyosin system, and the distribution of the waiting time between observed events was consistent with a Poisson process and the expected ATPase rate. Geometric constraints suggest a maximum of ∼26 nm of S2 can be unzipped from the filament, presumably involving disruption in the coiled-coil S2, a result consistent with observations by others of S2 protruding from the filament in muscle. We propose that sufficient force is available from the working heads in the filament to overcome the stiffness imposed by filament-S2 interactions.


Assuntos
Actinas , Pontos Quânticos , Músculo Liso , Miosinas , Miosinas de Músculo Liso
3.
Sci Adv ; 3(12): eaao2267, 2017 12.
Artigo em Inglês | MEDLINE | ID: mdl-29255801

RESUMO

In vitro motility assays, where purified myosin and actin move relative to one another, are used to better understand the mechanochemistry of the actomyosin adenosine triphosphatase (ATPase) cycle. We examined the relationship between the relative velocity (V) of actin and myosin and the number of available myosin heads (N) or [ATP] for smooth (SMM), skeletal (SKM), and cardiac (CMM) muscle myosin filaments moving over actin as well as V from actin filaments moving over a bed of monomeric SKM. These data do not fit well to a widely accepted model that predicts that V is limited by myosin detachment from actin (d/ton), where d equals step size and ton equals time a myosin head remains attached to actin. To account for these data, we have developed a mixed-kinetic model where V is influenced by both attachment and detachment kinetics. The relative contributions at a given V vary with the probability that a head will remain attached to actin long enough to reach the end of its flexible S2 tether. Detachment kinetics are affected by L/ton, where L is related to the tether length. We show that L is relatively long for SMM, SKM, and CMM filaments (59 ± 3 nm, 22 ± 9 nm, and 22 ± 2 nm, respectively). In contrast, L is shorter (8 ± 3 nm) when myosin monomers are attached to a surface. This suggests that the behavior of the S2 domain may be an important mechanical feature of myosin filaments that influences unloaded shortening velocities of muscle.


Assuntos
Modelos Biológicos , Músculo Esquelético/metabolismo , Músculo Liso/metabolismo , Miocárdio/metabolismo , Miosinas/metabolismo , Citoesqueleto de Actina/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Músculo Esquelético/citologia , Músculo Liso/citologia , Miocárdio/citologia , Miosina Tipo II/metabolismo , Coelhos
4.
Proc Natl Acad Sci U S A ; 112(36): 11235-40, 2015 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-26294254

RESUMO

It is not known which kinetic step in the acto-myosin ATPase cycle limits contraction speed in unloaded muscles (V0). Huxley's 1957 model [Huxley AF (1957) Prog Biophys Biophys Chem 7:255-318] predicts that V0 is limited by the rate that myosin detaches from actin. However, this does not explain why, as observed by Bárány [Bárány M (1967) J Gen Physiol 50(6, Suppl):197-218], V0 is linearly correlated with the maximal actin-activated ATPase rate (vmax), which is limited by the rate that myosin attaches strongly to actin. We have observed smooth muscle myosin filaments of different length and head number (N) moving over surface-attached F-actin in vitro. Fitting filament velocities (V) vs. N to a detachment-limited model using the myosin step size d=8 nm gave an ADP release rate 8.5-fold faster and ton (myosin's attached time) and r (duty ratio) ∼10-fold lower than previously reported. In contrast, these data were accurately fit to an attachment-limited model, V=N·v·d, over the range of N found in all muscle types. At nonphysiologically high N, V=L/ton rather than d/ton, where L is related to the length of myosin's subfragment 2. The attachment-limited model also fit well to the [ATP] dependence of V for myosin-rod cofilaments at three fixed N. Previously published V0 vs. vmax values for 24 different muscles were accurately fit to the attachment-limited model using widely accepted values for r and N, giving d=11.1 nm. Therefore, in contrast with Huxley's model, we conclude that V0 is limited by the actin-myosin attachment rate.


Assuntos
Citoesqueleto de Actina/metabolismo , Actomiosina/metabolismo , Contração Muscular , Miosinas/metabolismo , Citoesqueleto de Actina/química , Citoesqueleto de Actina/ultraestrutura , Actinas/química , Actinas/metabolismo , Actinas/ultraestrutura , Actomiosina/química , Actomiosina/ultraestrutura , Trifosfato de Adenosina/metabolismo , Trifosfato de Adenosina/farmacologia , Algoritmos , Animais , Galinhas , Cinética , Microscopia Eletrônica , Microscopia de Fluorescência/métodos , Modelos Biológicos , Músculo Liso/metabolismo , Miosinas/química , Miosinas/ultraestrutura , Ligação Proteica/efeitos dos fármacos , Coelhos , Rodaminas/química
5.
J Biol Chem ; 289(30): 21055-70, 2014 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-24907276

RESUMO

Actin-myosin interactions are well studied using soluble myosin fragments, but little is known about effects of myosin filament structure on mechanochemistry. We stabilized unphosphorylated smooth muscle myosin (SMM) and phosphorylated smooth muscle myosin (pSMM) filaments against ATP-induced depolymerization using a cross-linker and attached fluorescent rhodamine (XL-Rh-SMM). Electron micrographs showed that these side polar filaments are very similar to unmodified filaments. They are ~0.63 µm long and contain ~176 molecules. Rate constants for ATP-induced dissociation and ADP release from acto-myosin for filaments and S1 heads were similar. Actin-activated ATPases of SMM and XL-Rh-SMM were similarly regulated. XL-Rh-pSMM filaments moved processively on F-actin that was bound to a PEG brush surface. ATP dependence of filament velocities was similar to that for solution ATPases at high [actin], suggesting that both processes are limited by the same kinetic step (weak to strong transition) and therefore are attachment- limited. This differs from actin sliding over myosin monomers, which is primarily detachment-limited. Fitting filament data to an attachment-limited model showed that approximately half of the heads are available to move the filament, consistent with a side polar structure. We suggest the low stiffness subfragment 2 (S2) domain remains unhindered during filament motion in our assay. Actin-bound negatively displaced heads will impart minimal drag force because of S2 buckling. Given the ADP release rate, the velocity, and the length of S2, these heads will detach from actin before slack is taken up into a backwardly displaced high stiffness position. This mechanism explains the lack of detachment- limited kinetics at physiological [ATP]. These findings address how nonlinear elasticity in assemblies of motors leads to efficient collective force generation.


Assuntos
Citoesqueleto de Actina/química , Modelos Biológicos , Músculo Liso/química , Miosinas/química , Citoesqueleto de Actina/metabolismo , Difosfato de Adenosina/química , Difosfato de Adenosina/metabolismo , Trifosfato de Adenosina/química , Trifosfato de Adenosina/metabolismo , Animais , Galinhas , Cinética , Músculo Liso/metabolismo , Miosinas/metabolismo , Coelhos
6.
Arch Biochem Biophys ; 552-553: 74-82, 2014 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-24370736

RESUMO

To determine the mechanism by which sucrose slows in vitro actin sliding velocities, V, we used stopped flow kinetics and a single molecule binding assay, SiMBA. We observed that in the absence of ATP, sucrose (880mM) slowed the rate of actin-myosin (A-M) strong binding by 71±8% with a smaller inhibitory effect observed on spontaneous rigor dissociation (21±3%). Similarly, in the presence of ATP, sucrose slowed strong binding associated with Pi release by 85±9% with a smaller inhibitory effect on ATP-induced A-M dissociation, kT (39±2%). Sucrose had no noticeable effect on any other step in the ATPase reaction. In SiMBA, sucrose had a relatively small effect on the diffusion coefficient for actin fragments (25±2%), and with stopped flow we showed that sucrose increased the activation energy barrier for A-M strong binding by 37±3%, indicating that sucrose inhibits the rate of A-M strong binding by slowing bond formation more than diffusional searching. The inhibitory effects of sucrose on the rate of A-M rigor binding (71%) are comparable in magnitude to sucrose's effects on both V (79±33% decrease) and maximal actin-activated ATPase, kcat, (81±16% decrease), indicating that the rate of A-M strong bond formation significantly influences both kcat and V.


Assuntos
Actinas/metabolismo , Miosinas/metabolismo , Sacarose/farmacologia , Edulcorantes/farmacologia , Adenosina Trifosfatases/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Cinética , Ligação Proteica/efeitos dos fármacos , Coelhos
7.
Biochemistry ; 52(37): 6437-44, 2013 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-23947752

RESUMO

In striated muscle, calcium binding to the thin filament (TF) regulatory complex activates actin-myosin ATPase activity, and actin-myosin kinetics in turn regulates TF activation. However, a quantitative description of the effects of actin-myosin kinetics on the calcium sensitivity (pCa50) and cooperativity (nH) of TF activation is lacking. With the assumption that TF structural transitions and TF-myosin binding transitions are inextricably coupled, we advanced the principles established by Kad et al. [Kad, N., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 16990-16995] and Sich et al. [Sich, N. M., et al. (2011) J. Biol. Chem. 285, 39150-39159] to develop a simple model of TF regulation, which predicts that pCa50 varies linearly with duty ratio and that nH is maximal near physiological duty ratios. Using in vitro motility to determine the calcium sensitivity of TF sliding velocities, we measured pCa50 and nH at different myosin densities and in the presence of ATPase inhibitors. The observed effects of myosin density and actin-myosin duty ratio on pCa50 and nH are consistent with our model predictions. In striated muscle, pCa50 must match cytosolic calcium concentrations and a maximal nH optimizes calcium responsiveness. Our results indicate that pCa50 and nH can be predictably tuned through TF-myosin ATPase kinetics and that drugs and disease states that alter ATPase kinetics can, through their effects on calcium sensitivity, alter the efficiency of muscle contraction.


Assuntos
Citoesqueleto de Actina/fisiologia , Cálcio/fisiologia , Contração Muscular/fisiologia , Miosinas/metabolismo , Animais , Cinética , Cadeias de Markov , Modelos Biológicos , Método de Monte Carlo , Miosinas/química , Coelhos
8.
J Biol Chem ; 287(26): 22068-79, 2012 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-22549781

RESUMO

We examined the regulatory importance of interactions between regulatory light chain (RLC), essential light chain (ELC), and adjacent heavy chain (HC) in the regulatory domain of smooth muscle heavy meromyosin. After mutating the HC, RLC, and/or ELC to disrupt their predicted interactions (using scallop myosin coordinates), we measured basal ATPase, V(max), and K(ATPase) of actin-activated ATPase, actin-sliding velocities, rigor binding to actin, and kinetics of ATP binding and ADP release. If unphosphorylated, all mutants were similar to wild type showing turned-off behaviors. In contrast, if phosphorylated, mutation of RLC residues smM129Q and smG130C in the F-G helix linker, which interact with the ELC (Ca(2+) binding in scallop), was sufficient to abolish motility and diminish ATPase activity, without altering other parameters. ELC mutations within this interacting ELC loop (smR20M and smK25A) were normal, but smM129Q/G130C-R20M or -K25A showed a partially recovered phenotype suggesting that interaction between the RLC and ELC is important. A molecular dynamics study suggested that breaking the RLC/ELC interface leads to increased flexibility at the interface and ELC-binding site of the HC. We hypothesize that this leads to hampered activation by allowing a pre-existing equilibrium between activated and inhibited structural distributions (Vileno, B., Chamoun, J., Liang, H., Brewer, P., Haldeman, B. D., Facemyer, K. C., Salzameda, B., Song, L., Li, H. C., Cremo, C. R., and Fajer, P. G. (2011) Broad disorder and the allosteric mechanism of myosin II regulation by phosphorylation. Proc. Natl. Acad. Sci. U.S.A. 108, 8218-8223) to be biased strongly toward the inhibited distribution even when the RLC is phosphorylated. We propose that an important structural function of RLC phosphorylation is to promote or assist in the maintenance of an intact RLC/ELC interface. If the RLC/ELC interface is broken, the off-state structures are no longer destabilized by phosphorylation.


Assuntos
Músculo Liso/metabolismo , Cadeias Leves de Miosina/química , Subfragmentos de Miosina/química , Miosinas de Músculo Liso/química , Difosfato de Adenosina/química , Adenosina Trifosfatases/química , Sequência de Aminoácidos , Animais , Cálcio/química , Linhagem Celular , Galinhas , Humanos , Insetos , Cinética , Conformação Molecular , Dados de Sequência Molecular , Músculo Liso/citologia , Mutação , Fosforilação , Homologia de Sequência de Aminoácidos
9.
Proc Natl Acad Sci U S A ; 108(20): 8218-23, 2011 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-21536903

RESUMO

Double electron electron resonance EPR methods was used to measure the effects of the allosteric modulators, phosphorylation, and ATP, on the distances and distance distributions between the two regulatory light chain of myosin (RLC). Three different states of smooth muscle myosin (SMM) were studied: monomers, the short-tailed subfragment heavy meromyosin, and SMM filaments. We reconstituted myosin with nine single cysteine spin-labeled RLC. For all mutants we found a broad distribution of distances that could not be explained by spin-label rotamer diversity. For SMM and heavy meromyosin, several sites showed two heterogeneous populations in the unphosphorylated samples, whereas only one was observed after phosphorylation. The data were consistent with the presence of two coexisting heterogeneous populations of structures in the unphosphorylated samples. The two populations were attributed to an on and off state by comparing data from unphosphorylated and phosphorylated samples. Models of these two states were generated using a rigid body docking approach derived from EM [Wendt T, Taylor D, Trybus KM, Taylor K (2001) Proc Natl Acad Sci USA 98:4361-4366] (PNAS, 2001, 98:4361-4366), but our data revealed a new feature of the off-state, which is heterogeneity in the orientation of the two RLC. Our average off-state structure was very similar to the Wendt model reveal a new feature of the off state, which is heterogeneity in the orientations of the two RLC. As found previously in the EM study, our on-state structure was completely different from the off-state structure. The heads are splayed out and there is even more heterogeneity in the orientations of the two RLC.


Assuntos
Regulação Alostérica , Miosina Tipo II/metabolismo , Fosforilação/fisiologia , Miosinas de Músculo Liso/química , Trifosfato de Adenosina , Animais , Galinhas , Espectroscopia de Ressonância de Spin Eletrônica , Cadeias Leves de Miosina/metabolismo , Conformação Proteica , Marcadores de Spin
10.
Proc Natl Acad Sci U S A ; 108(4): 1421-6, 2011 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-21205888

RESUMO

The 10S self-inhibited monomeric conformation of myosin II has been characterized extensively in vitro. Based upon its structural and functional characteristics, it has been proposed to be an assembly-competent myosin pool in equilibrium with filaments in cells. It is known that myosin filaments can assemble and disassemble in nonmuscle cells, and in some smooth muscle cells, but whether or not the disassembled pool contains functional 10S myosin has not been determined. Here we address this question using human airway smooth muscle cells (hASMCs). Using two antibodies against different epitopes on smooth muscle myosin II (SMM), two distinct pools of SMM, diffuse, and stress-fiber-associated, were visualized by immunocytochemical staining. The two SMM pools were functional in that they could be interconverted in two ways: (i) by exposure to 10S- versus filament-promoting buffer conditions, and (ii) by exposure to a peptide that shifts the filament-10S equilibrium toward filaments in vitro by a known mechanism that requires the presence of the 10S conformation. The effect of the peptide was not due to a trivial increase in SMM phosphorylation, and its specificity was demonstrated by use of a scrambled peptide, which had no effect. Based upon these data, we conclude that hASMCs contain a significant pool of functional SMM in the 10S conformation that can assemble into filaments upon changing cellular conditions. This study provides unique direct evidence for the presence of a significant pool of functional myosin in the 10S conformation in cells.


Assuntos
Miócitos de Músculo Liso/metabolismo , Miosina Tipo II/química , Miosina Tipo II/metabolismo , Conformação Proteica , Citoesqueleto de Actina/metabolismo , Sequência de Aminoácidos , Western Blotting , Linhagem Celular Transformada , Permeabilidade da Membrana Celular/efeitos dos fármacos , Células Cultivadas , Citoesqueleto/metabolismo , Humanos , Imuno-Histoquímica , Microscopia Confocal , Modelos Biológicos , Modelos Moleculares , Dados de Sequência Molecular , Miócitos de Músculo Liso/efeitos dos fármacos , Peptídeos/farmacologia , Fosforilação/efeitos dos fármacos , Sistema Respiratório/citologia , Toxinas Biológicas/farmacologia
11.
J Biol Chem ; 285(50): 39150-9, 2010 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-20889979

RESUMO

Activation of thin filaments in striated muscle occurs when tropomyosin exposes myosin binding sites on actin either through calcium-troponin (Ca-Tn) binding or by actin-myosin (A-M) strong binding. However, the extent to which these binding events contributes to thin filament activation remains unclear. Here we propose a simple analytical model in which strong A-M binding and Ca-Tn binding independently activates the rate of A-M weak-to-strong binding. The model predicts how the level of activation varies with pCa as well as A-M attachment, N·k(att), and detachment, k(det), kinetics. To test the model, we use an in vitro motility assay to measure the myosin-based sliding velocities of thin filaments at different pCa, N·k(att), and k(det) values. We observe that the combined effects of varying pCa, N·k(att), and k(det) are accurately fit by the analytical model. The model and supporting data imply that changes in attachment and detachment kinetics predictably affect the calcium sensitivity of striated muscle mechanics, providing a novel A-M kinetic-based interpretation for perturbations (e.g. disease-related mutations) that alter calcium sensitivity.


Assuntos
Actinas/química , Cálcio/metabolismo , Miosinas/química , Citoesqueleto de Actina , Animais , Cálcio/química , Compostos Heterocíclicos de 4 ou mais Anéis/química , Cinética , Modelos Teóricos , Contração Muscular , Músculo Esquelético/metabolismo , Mutação , Coelhos , Tropomiosina/química , Troponina/química
12.
J Mol Biol ; 390(5): 879-92, 2009 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-19477187

RESUMO

A current popular model to explain phosphorylation of smooth muscle myosin (SMM) by myosin light-chain kinase (MLCK) proposes that MLCK is bound tightly to actin but weakly to SMM. We found that MLCK and calmodulin (CaM) co-purify with unphosphorylated SMM from chicken gizzard, suggesting that they are tightly bound. Although the MLCK:SMM molar ratio in SMM preparations was well below stoichiometric (1:73+/-9), the ratio was approximately 23-37% of that in gizzard tissue. Fifteen to 30% of MLCK was associated with CaM at approximately 1 nM free [Ca(2+)]. There were two MLCK pools that bound unphosphorylated SMM with K(d) approximately 10 and 0.2 microM and phosphorylated SMM with K(d) approximately 20 and 0.2 microM. Using an in vitro motility assay to measure actin sliding velocities, we showed that the co-purifying MLCK-CaM was activated by Ca(2+) and phosphorylation of SMM occurred at a pCa(50) of 6.1 and at a Hill coefficient of 0.9. Similar properties were observed from reconstituted MLCK-CaM-SMM. Using motility assays, co-sedimentation assays, and on-coverslip enzyme-linked immunosorbent assays to quantify proteins on the motility assay coverslip, we provide strong evidence that most of the MLCK is bound directly to SMM through the telokin domain and some may also be bound to both SMM and to co-purifying actin through the N-terminal actin-binding domain. These results suggest that this MLCK may play a role in the initiation of contraction.


Assuntos
Calmodulina/metabolismo , Complexos Multiproteicos/metabolismo , Quinase de Cadeia Leve de Miosina/metabolismo , Miosinas de Músculo Liso/metabolismo , Actinas/metabolismo , Trifosfato de Adenosina/farmacologia , Animais , Bovinos , Galinhas , Ensaio de Imunoadsorção Enzimática , Humanos , Cinética , Magnésio/farmacologia , Cadeias Leves de Miosina/metabolismo , Quinase de Cadeia Leve de Miosina/química , Quinase de Cadeia Leve de Miosina/farmacologia , Fragmentos de Peptídeos/farmacologia , Fosforilação/efeitos dos fármacos , Ligação Proteica/efeitos dos fármacos , Estrutura Terciária de Proteína
13.
Proc Natl Acad Sci U S A ; 105(26): 8938-43, 2008 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-18579780

RESUMO

Kinesin-1 is a molecular motor protein that transports cargo along microtubules. Inside cells, the vast majority of kinesin-1 is regulated to conserve ATP and to ensure its proper intracellular distribution and coordination with other molecular motors. Regulated kinesin-1 folds in half at a hinge in its coiled-coil stalk. Interactions between coiled-coil regions near the enzymatically active heads at the N terminus and the regulatory tails at the C terminus bring these globular elements in proximity and stabilize the folded conformation. However, it has remained a mystery how kinesin-1's microtubule-stimulated ATPase activity is regulated in this folded conformation. Here, we present evidence for a direct interaction between the kinesin-1 head and tail. We photochemically cross-linked heads and tails and produced an 8-A cryoEM reconstruction of the cross-linked head-tail complex on microtubules. These data demonstrate that a conserved essential regulatory element in the kinesin-1 tail interacts directly and specifically with the enzymatically critical Switch I region of the head. This interaction suggests a mechanism for tail-mediated regulation of the ATPase activity of kinesin-1. In our structure, the tail makes simultaneous contacts with the kinesin-1 head and the microtubule, suggesting the tail may both regulate kinesin-1 in solution and hold it in a paused state with high ADP affinity on microtubules. The interaction of the Switch I region of the kinesin-1 head with the tail is strikingly similar to the interactions of small GTPases with their regulators, indicating that other kinesin motors may share similar regulatory mechanisms.


Assuntos
Cinesinas/química , Cinesinas/metabolismo , Difosfato de Adenosina/metabolismo , Sequência de Aminoácidos , Reagentes de Ligações Cruzadas/farmacologia , Microscopia Crioeletrônica , Humanos , Cinesinas/efeitos da radiação , Cinesinas/ultraestrutura , Luz , Microtúbulos/efeitos dos fármacos , Microtúbulos/efeitos da radiação , Modelos Moleculares , Dados de Sequência Molecular , Proteínas Monoméricas de Ligação ao GTP/metabolismo , Ligação Proteica/efeitos dos fármacos , Ligação Proteica/efeitos da radiação , Estrutura Terciária de Proteína , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz
14.
J Biol Chem ; 282(7): 4336-4344, 2007 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-17121824

RESUMO

The effect of H(2)O(2) on smooth muscle heavy meromyosin (HMM) and subfragment 1 (S1) was examined. The number of molecules that retained the ability to bind ATP and the actinactivated rate of P(i) release were measured by single-turnover kinetics. H(2)O(2) treatment caused a decrease in HMM regulation from 800- to 27-fold. For unphosphorylated and phosphorylated heavy meromyosin and for S1, approximately 50% of the molecules lost the ability to bind to ATP. H(2)O(2) treatment in the presence of EDTA protected against ATPase inactivation and against the loss of total ATP binding. Inactivation of S1 versus time correlated to a loss of reactive thiols. Treatment of H(2)O(2)-inactivated phosphorylated HMM or S1 with dithiothreitol partially reactivated the ATPase but had no effect on total ATP binding. H(2)O(2)-inactivated S1 contained a prominent cross-link between the N-terminal 65-kDa and C-terminal 26-kDa heavy chain regions. Mass spectral studies revealed that at least seven thiols in the heavy chain and the essential light chain were oxidized to cysteic acid. In thiophosphorylated porcine tracheal muscle strips at pCa 9 + 2.1 mM ATP, H(2)O(2) caused a approximately 50% decrease in the amplitude but did not alter the rate of force generation, suggesting that H(2)O(2) directly affects the force generating complex. Dithiothreitol treatment reversed the H(2)O(2) inhibition of the maximal force by approximately 50%. These data, when compared with the in vitro kinetic data, are consistent with a H(2)O(2)-induced loss of functional myosin heads in the muscle.


Assuntos
Adenosina Trifosfatases/química , Trifosfato de Adenosina/química , Peróxido de Hidrogênio/química , Subfragmentos de Miosina/química , Miosinas de Músculo Liso/química , Actinas/química , Actinas/metabolismo , Adenosina Trifosfatases/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Cinética , Subfragmentos de Miosina/metabolismo , Fosforilação , Coelhos , Miosinas de Músculo Liso/metabolismo , Compostos de Sulfidrila/química , Compostos de Sulfidrila/metabolismo , Suínos , Traqueia/química , Traqueia/metabolismo
15.
J Biol Chem ; 281(50): 38801-11, 2006 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-17012238

RESUMO

In the presence of ATP, unphosphorylated smooth muscle myosin can form a catalytically inactive monomer that sediments at 10 Svedbergs (10 S). The tail of 10 S bends into thirds and interacts with the regulatory domain. ADP-P(i) is "trapped" at the active site, and consequently the ATPase activity is extremely low. We are interested in the structural basis for maintenance of this off state. Our prior photocross-linking work with 10 S showed that tail residues 1554-1583 are proximal to position 108 in the C-terminal lobe of one of the two regulatory light chains ( Olney, J. J., Sellers, J. R., and Cremo, C. R. (1996) J. Biol. Chem. 271, 20375-20384 ). These data suggested that the tail interacts with only one of the two regulatory light chains. Here we present data, using a photocross-linker on position 59 on the N-terminal lobe of the regulatory light chain (RLC), demonstrating that both regulatory light chains of a single molecule can cross-link to the light meromyosin portion of the tail. Mass spectrometric data show four specific cross-linked regions spanning residues 1428-1571 in the light meromyosin portion of the tail, consistent with cross-linking two RLC to one light meromyosin. In addition, we find that position 59 can cross-link internally to residues 42-45 within the same RLC subunit. The internal cross-link only forms in 10 S and not in unphosphorylated heavy meromyosin (lacking the light meromyosin), suggesting a structural rearrangement within the RLC attributed to the interaction of the tail with the head.


Assuntos
Músculo Liso/metabolismo , Miosinas/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Galinhas , Cromatografia em Gel , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Miosinas/química , Ligação Proteica , Conformação Proteica , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz
16.
J Biol Chem ; 279(38): 39905-14, 2004 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-15262959

RESUMO

Smooth muscle myosin can be switched on by phosphorylation of Ser-19 of the regulatory light chain. Our previous photocross-linking results suggested that an element of the structural mechanism for the regulatory switch was a phosphorylation-induced motion of the regulatory light chain N terminus (Wahlstrom, J. L., Randall, M. A., Jr., Lawson, J. D., Lyons, D. E., Siems, W. F., Crouch, G. J., Barr, R., Facemyer, K. C., and Cremo, C. R. (2003) J. Biol. Chem. 278, 5123-5131). Here we used three different approaches to test this notion, which are reactivity of cysteine thiols, pyrene and acrylodan spectral analysis, and pyrene fluorescence quenching. All methods detected significant differences between the unphosphorylated and phosphorylated regulatory light chain N termini in heavy meromyosin, a double-headed subfragment with an intact regulatory switch. These differences were not observed for subfragment-1, a single-headed, unregulated subfragment. In the presence of either ATP or ADP, phosphorylation increased the solvent exposure and decreased the polarity of the environment about position 23 of the regulatory light chain of heavy meromyosin. These phosphorylation-induced structural changes were not as evident in the absence of nucleotides. Nucleotide binding to unphosphorylated heavy meromyosin caused a decrease in exposure and an increase in polarity of the N terminus, whereas the effects of nucleotide on phosphorylated heavy meromyosin were the opposite. We showed a direct correlation between the kinetics of nucleotide binding/turnover and the conformational change reported by acrylodan at position 23 of the regulatory light chain. Acrylodan-A23C also reports the heads up (extended) to flexed (folded) transition in unphosphorylated heavy meromyosin. This is the first demonstration of direct coupling of nucleotide binding to conformational changes in the N terminus of the regulatory light chain.


Assuntos
2-Naftilamina/análogos & derivados , Músculo Liso/metabolismo , Cadeias Leves de Miosina/química , Cadeias Leves de Miosina/metabolismo , Miosinas de Músculo Liso/química , Miosinas de Músculo Liso/metabolismo , Actinas/metabolismo , Adenosina Trifosfatases/metabolismo , Sequência de Aminoácidos , Animais , Galinhas , Dados de Sequência Molecular , Cadeias Leves de Miosina/genética , Dobramento de Proteína , Estrutura Terciária de Proteína , Pirenos , Miosinas de Músculo Liso/genética , Espectrometria de Fluorescência
17.
J Biol Chem ; 278(7): 4410-5, 2003 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-12464606

RESUMO

The effect of ADP and phosphorylation upon the actin binding properties of heavy meromyosin was investigated using three fluorescence methods that monitor the number of heavy meromyosin heads that bind to pyrene-actin: (i) amplitudes of ATP-induced dissociation, (ii) amplitudes of ADP-induced dissociation of the pyrene-actin-heavy meromyosin complex, and (iii) amplitudes of the association of heavy meromyosin with pyrene-actin. Both heads bound to pyrene-actin, irrespective of regulatory light chain phosphorylation or the presence of ADP. This behavior was found for native regulated heavy meromyosin prepared by proteolytic digestion of chicken gizzard myosin with between 5 and 95% heavy chain cleavage at the actin-binding loop, showing that two-head binding is a property of heavy meromyosin with uncleaved heavy chains. These data are in contrast to a previous study using an uncleaved expressed preparation (Berger, C. E., Fagnant, P. M., Heizmann, S., Trybus, K. M., and Geeves, M. A. (2001) J. Biol. Chem. 276, 23240-23245), which showed that one head of the unphosphorylated heavy meromyosin-ADP complex bound to actin and that the partner head either did not bind or bound weakly. Possible explanations for the differences between the two studies are discussed. We have shown that unphosphorylated heavy meromyosin appears to adopt a special state in the presence of ADP based upon analysis of actin-heavy meromyosin association rate constants. Data were consistent with one head binding rapidly and the second head binding more slowly in the presence of ADP. Both heads bound to actin at the same rate for all other states.


Assuntos
Actinas/metabolismo , Difosfato de Adenosina/metabolismo , Músculo Liso/metabolismo , Subfragmentos de Miosina/metabolismo , Actinas/química , Animais , Sítios de Ligação , Galinhas , Fluorescência , Subfragmentos de Miosina/química , Fosforilação , Ligação Proteica
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