ATP-linked monomer-polymer equilibrium of smooth muscle myosin: the free folded monomer traps ADP.Pi.

Cross, Robert A.; Cross, KJ; Sobieszek, Apolinary

doi:10.1002/j.1460-2075.1986.tb04545.x

Cited by 83 publications

(62 citation statements)

References 22 publications

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“…It was found subsequently that dephosphorylated myosin monomers exist in a folded form, especially at low ionic strength (47,64,65), and phosphorylation of the light chain converts the folded myosins into extended ones, which are able to form filaments (7,56). It appears that a folded myosin monomer is able to trap the hydrolysis products of ATP (i.e., ADP and inorganic phosphate) and therefore is unable to consume ATP continuously (8,10). This could be an important in vivo mechanism for preventing monomeric myosins from utilizing ATP when they are not part of the thick filaments and not doing useful work.…”

Section: Molecular Mechanism Of Thick Filament Assembly In Vitro and mentioning

confidence: 99%

Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle

Seow

2005

American Journal of Physiology-Cell Physiology

111

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Seow, Chun Y. Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle. Am J Physiol Cell Physiol 289: C1363-C1368, 2005; doi:10.1152/ajpcell.00329.2005.-A major development in smooth muscle research in recent years is the recognition that the myofilament lattice of the muscle is malleable. The malleability appears to stem from plastic rearrangement of contractile and cytoskeletal filaments in response to stress and strain exerted on the muscle cell, and it allows the muscle to adapt to a wide range of cell lengths and maintain optimal contractility. Although much is still poorly understood, we have begun to comprehend some of the basic mechanisms underlying the assembly and disassembly of contractile and cytoskeletal filaments in smooth muscle during the process of adaptation to large changes in cell geometry. One factor that likely facilitates the plastic length adaptation is the ability of myosin filaments to form and dissolve at the right place and the right time within the myofilament lattice. It is proposed herein that formation of myosin filaments in vivo is aided by the various filament-stabilizing proteins, such as caldesmon, and that the thick filament length is determined by the dimension of the actin filament lattice. It is still an open question as to how the dimension of the dynamic filament lattice is regulated. In light of the new perspective of malleable myofilament lattice in smooth muscle, the roles of many smooth muscle proteins could be assigned or reassigned in the context of plastic reorganization of the contractile apparatus and cytoskeleton. contraction mechanism; length adaptation; thick filament; plasticity; contractile unit THE PRIMARY FUNCTION of smooth muscle in our bodies is to control and regulate the physical dimension and mechanical function of hollow organs. The large volume change in some organs requires that smooth muscle cells lining the organ wall have a large working length range. The length range over which a striated muscle can generate maximal or near maximal force is quite limited (19), between 10% and 20% of the resting muscle length. If smooth muscle were to have the same working length range, the corresponding volume change of the smooth muscle organ would be ϳ30 -70%, which is not adequate for organ functions such as emptying a urinary bladder or pushing a fetus through the birth canal.A broad plateau in the length-force relationship can be observed in many types of smooth muscle. It has been recognized recently that the plateau can become even broader if the muscle is allowed to adapt at each of the lengths at which force measurements are made (48, 69). Different extents of length adaptation in smooth muscle can be induced, at a fixed length, by a single contraction (21, 54), a series of brief activations (48, 55), or a continuous submaximal activation (42) over a period of tens of minutes. Adaptation can also occur in a relaxed muscle set at a fixed length over a period of hours (41, 69) or days (2, 44, 74). In isolated single cells from ...

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Section: Molecular Mechanism Of Thick Filament Assembly In Vitro and mentioning

confidence: 99%

Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle

Seow

2005

American Journal of Physiology-Cell Physiology

111

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“…The most striking example of this is the "trapping" of nucleotide at the active site when myosin adopts the folded monomeric conformation (Cross et al 1986), but chymotryptic HMM (Sellers, 1985) and dephosphorylated myosin filaments (Trybus, 1989) also show a strong inhibition of product release. Dephosphorylated SABL-HMM retained the ability to trap products, showing that foreign loops facilitate phosphate release only in the presence of actin.…”

Section: Chimeric Actin-binding Loops In Smooth Muscle Myosin 30262mentioning

confidence: 99%

Chimeric Substitutions of the Actin-binding Loop Activate Dephosphorylated but Not Phosphorylated Smooth Muscle Heavy Meromyosin

Rovner

Freyzon

Trybus

1995

Journal of Biological Chemistry

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Regulatory light chain (RLC) phosphorylation is necessary to activate smooth muscle myosin, unlike constitutively active striated muscle myosins. Here we show that an actin-binding surface loop located at the 50/20-kDa junction contributes to this fundamental difference between myosins. Substitution of the native actin-binding loop of smooth muscle heavy meromyosin (HMM) with that from either skeletal or ␤-cardiac myosin caused the chimeric HMMs to become unregulated like the myosin from which the loop was derived. Dephosphorylated chimeric HMMs gained the ability to move actin in a motility assay and had 50 -70% of the actinactivated ATPase activity of phosphorylated wild-type HMM. Direct binding measurements showed that the affinity of HMM for actin in the presence of MgATP was unaffected by loop substitution; thus the rate of a step other than binding is increased. Phosphorylation of the chimeras did not lead to a higher V max than obtained for wild-type HMM. In the absence of actin, a foreign loop did not affect nucleotide trapping. Native regulated molecules have thus evolved a loop sequence which prevents rapid product release by actin when the RLC is dephosphorylated, thereby allowing activity to be controlled by RLC phosphorylation.Myosins differ from each other in how fast they can move actin, the rates of their actin-activated ATPases, and whether or not these activities are regulated. It has been recently suggested that a divergent surface loop at the actin-binding interface "tunes" the rate of phosphate release and thus sets the maximum velocity (V max ) for ATPase activity. A second loop, at the 25/50-kDa interface near the ATP-binding site, was proposed to control the rate of ADP release and thus be responsible for determining the velocity at which different myosins move actin (Spudich, 1994). The actin-activated ATPase activity of a chimeric Dictyostelium myosin containing the actin-binding loop from skeletal muscle myosin was 5-fold higher than wildtype Dictyostelium myosin, providing experimental evidence in support of the first part of this hypothesis (Uyeda et al., 1994). This study did not show if such a generalization would hold true for other myosin motors nor was the question of heavy chain sequences involved in regulation of activity addressed.The molecular step that is controlled by light chain phosphorylation in smooth muscle myosin is phosphate release from the active site (Sellers, 1985). It has been recently proposed that myosin is a "back door" enzyme, whereby the cleaved phosphate leaves via a cleft in the 50-kDa domain, instead of through the nucleotide-binding pocket from which it entered. Binding of actin is suggested to promote movement of the highly conserved P-loop near the active site so that phosphate can leave (Yount et al., 1995). The interaction of actin with myosin probably involves several steps; the first is thought to be a weak interaction between the N terminus of actin and the 50/20-kDa junction of myosin, followed by stronger interactions involving hydrophobic res...

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“…The relationship of SHl and SH2 to sequence B would also be consistent with other well characterized observations accompanying their modification such as changes in the ATPase properties [ 191, trapping of Mg nucleotide and MgPPi when they are covalently bridged [20], changes in their separation on addition of MgADP [21-231 and changes in their reactivities induced by binding of nucleotide [24,25]. It is of interest to note that modification of the equivalent thiols in the 25-kDa C-terminal segment of smooth myosin Sl abolishes the formation of the 10s conformation [26] usually associated with trapping of MgATP [27]. Furthermore, this location for sequence B would also be at a recently defined actin contact near SHl [28], consistent with the well known communication between the ATPase and actin sites.…”

Section: Resultsmentioning

confidence: 99%

A second consensus sequence of ATP‐requiring proteins resides in the 21‐kDa C‐terminal segment of myosin subfragment 1

Burke¹,

Rajasekharan²,

Maruta³

et al. 1990

FEBS Letters

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Previous comparisons of sequence homologies of ATP‐requiring enzymes have defined three consensus sequences which appear to be involved in the binding of the nucleotide. One of these was identified in the N‐terminal 27‐kDa segment of the myosin heavy chain but the other two sequences have not hitherto been located in myosin. The present paper proposes that one of these other two consensus sequences is in the 21‐kDa C‐terminal portion of S1 and that it may contribute to the ATP binding domain.

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ATP-linked monomer-polymer equilibrium of smooth muscle myosin: the free folded monomer traps ADP.Pi.

Cited by 83 publications

References 22 publications

Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle

Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle

Chimeric Substitutions of the Actin-binding Loop Activate Dephosphorylated but Not Phosphorylated Smooth Muscle Heavy Meromyosin

A second consensus sequence of ATP‐requiring proteins resides in the 21‐kDa C‐terminal segment of myosin subfragment 1

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