Journal articles: 'Myosin mechanics'

1

Surcel, Alexandra, Win Pin Ng, Hoku West-Foyle, Qingfeng Zhu, Yixin Ren, Lindsay B. Avery, Agata K. Krenc, et al. "Pharmacological activation of myosin II paralogs to correct cell mechanics defects." Proceedings of the National Academy of Sciences 112, no. 5 (January 20, 2015): 1428–33. http://dx.doi.org/10.1073/pnas.1412592112.

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Current approaches to cancer treatment focus on targeting signal transduction pathways. Here, we develop an alternative system for targeting cell mechanics for the discovery of novel therapeutics. We designed a live-cell, high-throughput chemical screen to identify mechanical modulators. We characterized 4-hydroxyacetophenone (4-HAP), which enhances the cortical localization of the mechanoenzyme myosin II, independent of myosin heavy-chain phosphorylation, thus increasing cellular cortical tension. To shift cell mechanics, 4-HAP requires myosin II, including its full power stroke, specifically activating human myosin IIB (MYH10) and human myosin IIC (MYH14), but not human myosin IIA (MYH9). We further demonstrated that invasive pancreatic cancer cells are more deformable than normal pancreatic ductal epithelial cells, a mechanical profile that was partially corrected with 4-HAP, which also decreased the invasion and migration of these cancer cells. Overall, 4-HAP modifies nonmuscle myosin II-based cell mechanics across phylogeny and disease states and provides proof of concept that cell mechanics offer a rich drug target space, allowing for possible corrective modulation of tumor cell behavior.

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Farman, Gerrie P., Priya Muthu, Katarzyna Kazmierczak, Danuta Szczesna-Cordary, and Jeffrey R. Moore. "Impact of familial hypertrophic cardiomyopathy-linked mutations in the NH2 terminus of the RLC on β-myosin cross-bridge mechanics." Journal of Applied Physiology 117, no. 12 (December 15, 2014): 1471–77. http://dx.doi.org/10.1152/japplphysiol.00798.2014.

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Familial hypertrophic cardiomyopathy (HCM) is associated with mutations in sarcomeric proteins, including the myosin regulatory light chain (RLC). Here we studied the impact of three HCM mutations located in the NH2 terminus of the RLC on the molecular mechanism of β-myosin heavy chain (MHC) cross-bridge mechanics using the in vitro motility assay. To generate mutant β-myosin, native RLC was depleted from porcine cardiac MHC and reconstituted with mutant (A13T, F18L, and E22K) or wild-type (WT) human cardiac RLC. We characterized the mutant myosin force and motion generation capability in the presence of a frictional load. Compared with WT, all three mutants exhibited reductions in maximal actin filament velocity when tested under low or no frictional load. The actin-activated ATPase showed no significant difference between WT and HCM-mutant-reconstituted myosins. The decrease in velocity has been attributed to a significantly increased duty cycle, as was measured by the dependence of actin sliding velocity on myosin surface density, for all three mutant myosins. These results demonstrate a mutation-induced alteration in acto-myosin interactions that may contribute to the pathogenesis of HCM.

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Hoh, Joseph F. Y. "`Superfast' or masticatory myosin and the evolution of jaw-closing muscles of vertebrates." Journal of Experimental Biology 205, no. 15 (August 1, 2002): 2203–10. http://dx.doi.org/10.1242/jeb.205.15.2203.

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SUMMARY There are four fibre types in mammalian limb muscles, each expressing a different myosin isoform that finely tunes fibre mechanics and energetics for locomotion. Functional demands on jaw-closer muscles are complex and varied,and jaw muscles show considerable phylogenetic plasticity, with a repertoire for myosin expression that includes limb, developmental, α-cardiac and masticatory myosins. Masticatory myosin is a phylogenetically ancient motor with distinct light chains and heavy chains. It confers high maximal muscle force and power. It is highly jaw-specific in expression and is found in several orders of eutherian and marsupial mammals including carnivores,chiropterans, primates, dasyurids and diprotodonts. In exceptional species among these orders, masticatory myosin is replaced by some other isoform. Masticatory myosin is also found in reptiles and fish. It is postulated that masticatory myosin diverged early during gnathostome evolution and is expressed in primitive mammals. During mammalian evolution, mastication of food became important, and in some taxa jaw closers replaced masticatory myosin with α-cardiac, developmental, slow or fast limb myosins to adapt to the variety of diets and eating habits. This occurred early in some taxa(rodents, ungulates) and later in others (macropods, lesser panda, humans). The cellular basis for the uniqueness of jaw-closing muscles lies in their developmental origin.

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Buttrick, P. M., A. Malhotra, and J. Scheuer. "Effects of systolic overload and swim training on cardiac mechanics and biochemistry in rats." Journal of Applied Physiology 64, no. 4 (April 1, 1988): 1466–71. http://dx.doi.org/10.1152/jappl.1988.64.4.1466.

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We have previously shown that swim conditioning corrects the depressed mechanical function and myosin adenosinetriphosphatase (ATPase) activities associated with renovascular hypertension (HTN) in the rat. The present study was designed to assess the effects of swim conditioning on another form of systolic overload, subdiaphragmatic suprarenal aortic stenosis. Cardiac mechanics in an isolated working heart apparatus and myosin enzymology were studied in four groups of rats: controls (C), animals with chronic systolic overload secondary to aortic constriction (St), swim-conditioning animals (Sw), and animals exposed to a combined load (St-Sw). Heart weight was increased by 23% in St, 27% in Sw, and 36% in St-Sw. In contrast to HTN, cardiac pump and muscle function were not depressed in St. Sw was associated with improved cardiac output, stroke work, and velocity of circumferential fiber shortening. St-Sw showed improved mechanical cardiac performance relative to both C and St. The percent of ventricular myosin of the V1 type and Ca2+-activated myosin ATPase activity relative to C was unchanged in Sw but was depressed in St and St-Sw. These data demonstrate that the salutory mechanical effects of Sw can be superimposed on the systolic overload of St. However, the dissociation between mechanics and myosin enzymology suggests that factors in excitation-contraction coupling other than myosin isoenzyme shifts are responsible for this finding.

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Lee, Stacey, and Sanjay Kumar. "Actomyosin stress fiber mechanosensing in 2D and 3D." F1000Research 5 (September 7, 2016): 2261. http://dx.doi.org/10.12688/f1000research.8800.1.

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Mechanotransduction is the process through which cells survey the mechanical properties of their environment, convert these mechanical inputs into biochemical signals, and modulate their phenotype in response. These mechanical inputs, which may be encoded in the form of extracellular matrix stiffness, dimensionality, and adhesion, all strongly influence cell morphology, migration, and fate decisions. One mechanism through which cells on planar or pseudo-planar matrices exert tensile forces and interrogate microenvironmental mechanics is through stress fibers, which are bundles composed of actin filaments and, in most cases, non-muscle myosin II filaments. Stress fibers form a continuous structural network that is mechanically coupled to the extracellular matrix through focal adhesions. Furthermore, myosin-driven contractility plays a central role in the ability of stress fibers to sense matrix mechanics and generate tension. Here, we review the distinct roles that non-muscle myosin II plays in driving mechanosensing and focus specifically on motility. In a closely related discussion, we also describe stress fiber classification schemes and the differing roles of various myosin isoforms in each category. Finally, we briefly highlight recent studies exploring mechanosensing in three-dimensional environments, in which matrix content, structure, and mechanics are often tightly interrelated. Stress fibers and the myosin motors therein represent an intriguing and functionally important biological system in which mechanics, biochemistry, and architecture all converge.

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Picariello, Hannah S., Rajappa S. Kenchappa, Vandana Rai, James F. Crish, Athanassios Dovas, Katarzyna Pogoda, Mariah McMahon, et al. "Myosin IIA suppresses glioblastoma development in a mechanically sensitive manner." Proceedings of the National Academy of Sciences 116, no. 31 (June 24, 2019): 15550–59. http://dx.doi.org/10.1073/pnas.1902847116.

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The ability of glioblastoma to disperse through the brain contributes to its lethality, and blocking this behavior has been an appealing therapeutic approach. Although a number of proinvasive signaling pathways are active in glioblastoma, many are redundant, so targeting one can be overcome by activating another. However, these pathways converge on nonredundant components of the cytoskeleton, and we have shown that inhibiting one of these—the myosin II family of cytoskeletal motors—blocks glioblastoma invasion even with simultaneous activation of multiple upstream promigratory pathways. Myosin IIA and IIB are the most prevalent isoforms of myosin II in glioblastoma, and we now show that codeleting these myosins markedly impairs tumorigenesis and significantly prolongs survival in a rodent model of this disease. However, while targeting just myosin IIA also impairs tumor invasion, it surprisingly increases tumor proliferation in a manner that depends on environmental mechanics. On soft surfaces myosin IIA deletion enhances ERK1/2 activity, while on stiff surfaces it enhances the activity of NFκB, not only in glioblastoma but in triple-negative breast carcinoma and normal keratinocytes as well. We conclude myosin IIA suppresses tumorigenesis in at least two ways that are modulated by the mechanics of the tumor and its stroma. Our results also suggest that inhibiting tumor invasion can enhance tumor proliferation and that effective therapy requires targeting cellular components that drive both proliferation and invasion simultaneously.

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Bates, Genevieve, Sara Sigurdardottir, Linda Kachmar, Nedjma B. Zitouni, Andrea Benedetti, Basil J. Petrof, Dilson Rassier, and Anne-Marie Lauzon. "Molecular, cellular, and muscle strip mechanics of the mdx mouse diaphragm." American Journal of Physiology-Cell Physiology 304, no. 9 (May 1, 2013): C873—C880. http://dx.doi.org/10.1152/ajpcell.00220.2012.

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Duchenne muscular dystrophy (DMD) is a lethal disorder caused by defects in the dystrophin gene, which leads to respiratory or cardiac muscle failure. Lack of dystrophin predisposes the muscle cell sarcolemmal membrane to mechanical damage. However, the role of myosin in this muscle weakness has been poorly addressed. In the current study, in addition to measuring the velocity of actin filament propulsion (υmax) of mdx myosin molecules purified from 3- and 12-mo-old control (C57Bl/10) and mdx (C57Bl/10 mdx) mouse diaphragms, we also measured myosin force production. Furthermore, we measured cellular and muscle strip force production at three mo of age. Stress (force/cross-sectional area) was smaller for mdx than control at the muscle strip level but was not different at the single fiber level. υmax of mdx myosin was not different from control at either 3 or 12 mo nor was their relative myosin force. The type I and IIb myosin heavy chain composition was not different between control and mdx diaphragms at 3 or 12 mo. These results suggest that the myosin function, as well as the single fiber mechanics, do not underlie the weakness of the mdx diaphragm. This weakness was only observed at the level of the intact muscle bundle and could not be narrowed down to a specific mechanical impairment of its individual fibers or myosin molecules.

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8

Alpert, Norman R., Christine Brosseau, Andrea Federico, Maike Krenz, Jeffrey Robbins, and David M. Warshaw. "Molecular mechanics of mouse cardiac myosin isoforms." American Journal of Physiology-Heart and Circulatory Physiology 283, no. 4 (October 1, 2002): H1446—H1454. http://dx.doi.org/10.1152/ajpheart.00274.2002.

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Two myosin isoforms are expressed in myocardium, αα-homodimers (V1) and ββ-homodimers (V3). V1exhibits higher velocities and myofibrillar ATPase activities compared with V3. We also observed this for cardiac myosin from normal (V1) and propylthiouracil-treated (V3) mice. Actin velocity in a motility assay ( V actin) over V1 myosin was twice that of V3 as was the myofibrillar ATPase. Myosin's average force (Favg) was similar for V1 and V3. Comparing V actin and Favg across species for both V1 and V3, our laboratory showed previously (VanBuren P, Harris DE, Alpert NR, and Warshaw DM. Circ Res 77: 439–444, 1995) that mouse V1 has greater V actin and Favg compared with rabbit V1. Mouse V3 V actin was twice that of rabbit V actin. To understand myosin's molecular structure and function, we compared α- and β-cardiac myosin sequences from rodents and rabbits. The rabbit α- and β-cardiac myosin differed by eight and four amino acids, respectively, compared with rodents. These residues are localized to both the motor domain and the rod. These differences in sequence and mechanical performance may be an evolutionary attempt to match a myosin's mechanical behavior to the heart's power requirements.

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9

Veigel, Claudia, and James R. Sellers. "Mechanics of myosin V near stall." Biophysical Journal 96, no. 3 (February 2009): 138a. http://dx.doi.org/10.1016/j.bpj.2008.12.3865.

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10

Siththanandan, Verl B., Yasuharu Takagi, Yi Yang, Davin K. T. Hong, and James R. Sellers. "Characterization of drosophila myosin 7a mechanics." Biophysical Journal 96, no. 3 (February 2009): 141a. http://dx.doi.org/10.1016/j.bpj.2008.12.3878.

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11

Yanagida, T., S. Esaki, A. Hikikoshi Iwane, Y. Inoue, A. Ishijima, K. Kitamura, H. Tanaka, and M. Tokunaga. "Single–motor mechanics and models of the myosin motor." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 355, no. 1396 (April 29, 2000): 441–47. http://dx.doi.org/10.1098/rstb.2000.0585.

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Recent progress in single–molecule detection techniques is remarkable. These techniques have allowed the accurate determination of myosin–head–induced displacements and how mechanical cycles are coupled to ATP hydrolysis, by measuring individual mechanical events and chemical events of actomyosin directly at the single–molecule level. Here we review our recent work in which we have made detailed measurements of myosin step size and mechanochemical coupling, and propose a model of the myosin motor.

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12

Caremani, Marco, and Massimo Reconditi. "Anisotropic Elasticity of the Myosin Motor in Muscle." International Journal of Molecular Sciences 23, no. 5 (February 25, 2022): 2566. http://dx.doi.org/10.3390/ijms23052566.

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To define the mechanics and energetics of the myosin motor action in muscles, it is mandatory to know fundamental parameters such as the stiffness and the force of the single myosin motor, and the fraction of motors attached during contraction. These parameters can be defined in situ using sarcomere−level mechanics in single muscle fibers under the assumption that the stiffness of a myosin dimer with both motors attached (as occurs in rigor, when all motors are attached) is twice that of a single motor (as occurs in the isometric contraction). We use a mechanical/structural model to identify the constraints that underpin the stiffness of the myosin dimer with both motors attached to actin. By comparing the results of the model with the data in the literature, we conclude that the two-fold axial stiffness of the dimers with both motors attached is justified by a stiffness of the myosin motor that is anisotropic and higher along the axis of the myofilaments. A lower azimuthal stiffness of the motor plays an important role in the complex architecture of the sarcomere by allowing the motors to attach to actin filaments at different azimuthal angles relative to the thick filament.

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Huxley, A. F. "Mechanics and models of the myosin motor." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 355, no. 1396 (April 29, 2000): 433–40. http://dx.doi.org/10.1098/rstb.2000.0584.

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In striated muscles, shortening comes about by the sliding movement of thick filaments, composed mostly of myosin, relative to thin filaments, composed mostly of actin. This is brought about by cyclic action of ‘cross–bridges’ composed of the heads of myosin molecules projecting from a thick filament, which attach to an adjacent thin filament, exert force for a limited time and detach, and then repeat this cycle further along the filament. The requisite energy is provided by the hydrolysis of a molecule of adenosine triphosphate to the diphosphate and inorganic phosphate, the steps of this reaction being coupled to mechanical events within the cross–bridge. The nature of these events is discussed. There is good evidence that one of them is a change in the angle of tilt of a ‘lever arm’ relative to the ‘catalytic domain’ of the myosin head which binds to the actin filament. It is suggested here that this event is superposed on a slower, temperature–sensitive change in the orientation of the catalytic domain on the actin filament. Many uncertainties remain.

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Baker, Josh E. "Saturation of Actin-Myosin Kinetics and Mechanics." Biophysical Journal 120, no. 3 (February 2021): 60a. http://dx.doi.org/10.1016/j.bpj.2020.11.596.

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Ohnuki, Y., Y. Kunioka, M. Ohtsuki, T. Yamada, Y. Saeki, and K. yanagisawa. "1P170 Molecular mechanics of masticatory muscle myosin." Seibutsu Butsuri 44, supplement (2004): S72. http://dx.doi.org/10.2142/biophys.44.s72_2.

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Baker, Josh E. "The collective mechanics of myosin in muscle." Biophysical Journal 96, no. 3 (February 2009): 554a. http://dx.doi.org/10.1016/j.bpj.2008.12.3638.

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Guilford, William H., and David M. Warshaw. "The molecular mechanics of smooth muscle myosin." Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology 119, no. 3 (March 1998): 451–58. http://dx.doi.org/10.1016/s0305-0491(98)00002-9.

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Larson, Stephanie M., Hyo J. Lee, Pei-hsuan Hung, Lauren M. Matthews, Douglas N. Robinson, and Janice P. Evans. "Cortical Mechanics and Meiosis II Completion in Mammalian Oocytes Are Mediated by Myosin-II and Ezrin-Radixin-Moesin (ERM) Proteins." Molecular Biology of the Cell 21, no. 18 (September 15, 2010): 3182–92. http://dx.doi.org/10.1091/mbc.e10-01-0066.

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Cell division is inherently mechanical, with cell mechanics being a critical determinant governing the cell shape changes that accompany progression through the cell cycle. The mechanical properties of symmetrically dividing mitotic cells have been well characterized, whereas the contribution of cellular mechanics to the strikingly asymmetric divisions of female meiosis is very poorly understood. Progression of the mammalian oocyte through meiosis involves remodeling of the cortex and proper orientation of the meiotic spindle, and thus we hypothesized that cortical tension and stiffness would change through meiotic maturation and fertilization to facilitate and/or direct cellular remodeling. This work shows that tension in mouse oocytes drops about sixfold during meiotic maturation from prophase I to metaphase II and then increases ∼1.6-fold upon fertilization. The metaphase II egg is polarized, with tension differing ∼2.5-fold between the cortex over the meiotic spindle and the opposite cortex, suggesting that meiotic maturation is accompanied by assembly of a cortical domain with stiffer mechanics as part of the process to achieve asymmetric cytokinesis. We further demonstrate that actin, myosin-II, and the ERM (Ezrin/Radixin/Moesin) family of proteins are enriched in complementary cortical domains and mediate cellular mechanics in mammalian eggs. Manipulation of actin, myosin-II, and ERM function alters tension levels and also is associated with dramatic spindle abnormalities with completion of meiosis II after fertilization. Thus, myosin-II and ERM proteins modulate mechanical properties in oocytes, contributing to cell polarity and to completion of meiosis.

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Karabina, Anastasia, Priya Muthu, Katarzyna Kazmierczak, Danuta Szczesna-Cordary, and Jeffrey Moore. "The Effect of Myosin Regulatory Light Chain Phosphorylation on N47K Mutant Myosin Mechanics." Biophysical Journal 106, no. 2 (January 2014): 563a. http://dx.doi.org/10.1016/j.bpj.2013.11.3126.

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Moore, Jeffrey R., Elena B. Krementsova, Kathleen M. Trybus, and David M. Warshaw. "Myosin V exhibits a high duty cycle and large unitary displacement." Journal of Cell Biology 155, no. 4 (November 12, 2001): 625–36. http://dx.doi.org/10.1083/jcb.200103128.

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Myosin V is a double-headed unconventional myosin that has been implicated in organelle transport. To perform this role, myosin V may have a high duty cycle. To test this hypothesis and understand the properties of this molecule at the molecular level, we used the laser trap and in vitro motility assay to characterize the mechanics of heavy meromyosin–like fragments of myosin V (M5HMM) expressed in the Baculovirus system. The relationship between actin filament velocity and the number of interacting M5HMM molecules indicates a duty cycle of ≥50%. This high duty cycle would allow actin filament translocation and thus organelle transport by a few M5HMM molecules. Single molecule displacement data showed predominantly single step events of 20 nm and an occasional second step to 37 nm. The 20-nm unitary step represents the myosin V working stroke and is independent of the mode of M5HMM attachment to the motility surface or light chain content. The large M5HMM working stroke is consistent with the myosin V neck acting as a mechanical lever. The second step is characterized by an increased displacement variance, suggesting a model for how the two heads of myosin V function in processive motion.

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Wakatsuki, T. "Mechanics of cell spreading: role of myosin II." Journal of Cell Science 116, no. 8 (March 4, 2003): 1617–25. http://dx.doi.org/10.1242/jcs.00340.

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Sellers, James R., John Kendrick-Jones, and Claudia Veigel. "Single Molecule Mechanics Of Myosin Motors Under Load." Biophysical Journal 96, no. 3 (February 2009): 553a. http://dx.doi.org/10.1016/j.bpj.2008.12.3636.

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23

Norstrom, Melanie F., Philip A. Smithback, and Ronald S. Rock. "Unconventional Processive Mechanics of Non-muscle Myosin IIB." Journal of Biological Chemistry 285, no. 34 (May 29, 2010): 26326–34. http://dx.doi.org/10.1074/jbc.m110.123851.

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Jiang, Ming Ya, and Michael P. Sheetz. "Mechanics of myosin motor: Force and step size." BioEssays 16, no. 8 (August 1994): 531–32. http://dx.doi.org/10.1002/bies.950160803.

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Wang, Yihua, Katalin Ajtai, and Thomas P. Burghardt. "Cardiac and skeletal actin substrates uniquely tune cardiac myosin strain-dependent mechanics." Open Biology 8, no. 11 (November 2018): 180143. http://dx.doi.org/10.1098/rsob.180143.

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Cardiac ventricular myosin (βmys) translates actin by transducing ATP free energy into mechanical work during muscle contraction. Unitary βmys translation of actin is the step-size. In vitro and in vivo βmys regulates contractile force and velocity autonomously by remixing three different step-sizes with adaptive stepping frequencies. Cardiac and skeletal actin isoforms have a specific 1 : 4 stoichiometry in normal adult human ventriculum. Human adults with inheritable hypertrophic cardiomyopathy (HCM) upregulate skeletal actin in ventriculum probably compensating the diseased muscle's inability to meet demand by adjusting βmys force–velocity characteristics. βmys force–velocity characteristics were compared for skeletal versus cardiac actin substrates using ensemble in vitro motility and single myosin assays. Two competing myosin strain-sensitive mechanisms regulate step-size choices dividing single βmys mechanics into low- and high-force regimes. The actin isoforms alter myosin strain-sensitive regulation such that onset of the high-force regime, where a short step-size is a large or major contributor, is offset to higher loads probably by the unique cardiac essential light chain (ELC) N-terminus/cardiac actin contact at Glu6/Ser358. It modifies βmys force–velocity by stabilizing the ELC N-terminus/cardiac actin association. Uneven onset of the high-force regime for skeletal versus cardiac actin modulates force–velocity characteristics as skeletal/cardiac actin fractional content increases in diseased muscle.

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Khokhlova, Anastasia, Tatiana Myachina, Denis Volzhaninov, Xenia Butova, Anastasia Kochurova, Valentina Berg, Irina Gette, et al. "Type 1 Diabetes Impairs Cardiomyocyte Contractility in the Left and Right Ventricular Free Walls but Preserves It in the Interventricular Septum." International Journal of Molecular Sciences 23, no. 3 (February 2, 2022): 1719. http://dx.doi.org/10.3390/ijms23031719.

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Type 1 diabetes (T1D) leads to ischemic heart disease and diabetic cardiomyopathy. We tested the hypothesis that T1D differently affects the contractile function of the left and right ventricular free walls (LV, RV) and the interventricular septum (IS) using a rat model of alloxan-induced T1D. Single-myocyte mechanics and cytosolic Ca2+ concentration transients were studied on cardiomyocytes (CM) from LV, RV, and IS in the absence and presence of mechanical load. In addition, we analyzed the phosphorylation level of sarcomeric proteins and the characteristics of the actin-myosin interaction. T1D similarly affected the characteristics of actin-myosin interaction in all studied regions, decreasing the sliding velocity of native thin filaments over myosin in an in vitro motility assay and its Ca2+ sensitivity. A decrease in the thin-filament velocity was associated with increased expression of β-myosin heavy-chain isoform. However, changes in the mechanical function of single ventricular CM induced by T1D were different. T1D depressed the contractility of CM from LV and RV; it decreased the auxotonic tension amplitude and the slope of the active tension–length relationship. Nevertheless, the contractile function of CM from IS was principally preserved.

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Squire, John. "Special Issue: The Actin-Myosin Interaction in Muscle: Background and Overview." International Journal of Molecular Sciences 20, no. 22 (November 14, 2019): 5715. http://dx.doi.org/10.3390/ijms20225715.

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Muscular contraction is a fundamental phenomenon in all animals; without it life as we know it would be impossible. The basic mechanism in muscle, including heart muscle, involves the interaction of the protein filaments myosin and actin. Motility in all cells is also partly based on similar interactions of actin filaments with non-muscle myosins. Early studies of muscle contraction have informed later studies of these cellular actin-myosin systems. In muscles, projections on the myosin filaments, the so-called myosin heads or cross-bridges, interact with the nearby actin filaments and, in a mechanism powered by ATP-hydrolysis, they move the actin filaments past them in a kind of cyclic rowing action to produce the macroscopic muscular movements of which we are all aware. In this special issue the papers and reviews address different aspects of the actin-myosin interaction in muscle as studied by a plethora of complementary techniques. The present overview provides a brief and elementary introduction to muscle structure and function and the techniques used to study it. It goes on to give more detailed descriptions of what is known about muscle components and the cross-bridge cycle using structural biology techniques, particularly protein crystallography, electron microscopy and X-ray diffraction. It then has a quick look at muscle mechanics and it summarises what can be learnt about how muscle works based on the other studies covered in the different papers in the special issue. A picture emerges of the main molecular steps involved in the force-producing process; steps that are also likely to be seen in non-muscle myosin interactions with cellular actin filaments. Finally, the remarkable advances made in studying the effects of mutations in the contractile assembly in causing specific muscle diseases, particularly those in heart muscle, are outlined and discussed.

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Buttrick, P., C. Perla, A. Malhotra, D. Geenen, M. Lahorra, and J. Scheuer. "Effects of chronic dobutamine on cardiac mechanics and biochemistry after myocardial infarction in rats." American Journal of Physiology-Heart and Circulatory Physiology 260, no. 2 (February 1, 1991): H473—H479. http://dx.doi.org/10.1152/ajpheart.1991.260.2.h473.

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After myocardial infarction in rats, muscle performance in the remaining hypertrophied myocardium deteriorates and is associated with a decrease in myosin adenosinetriphosphatase (ATPase) activity and a shift to the V3 myosin heavy-chain isoform. We have previously shown in another model of hypertrophy, secondary to renovascular hypertension, that chronic intermittent adrenergic stimulation with dobutamine (Db) can prevent this biochemical adaptation. The present study was undertaken to assess the effects of chronic Db treatment on cardiac mass, function, metabolism, and myosin biochemistry in animals subjected to chronic myocardial infarction. Four groups of rats were studied: controls, animals treated with Db (2 mg/kg 2X daily for 4 wk), animals subjected to myocardial infarction and killed after 4 wk (MI), and MI animals concurrently treated with Db for 4 wk (MI-Db). The two MI groups were subdivided into those with and without congestive heart failure (CHF). Heart weight was increased by 13% with Db, unchanged in the infarct groups without CHF, and increased by 9 and 22% in the infarct groups with CHF. Db did not have any additional effect on heart weight in these later groups. Infarct weight was greatest in the animals with CHF, and viable myocardium was equivalent in all infarct groups suggesting that CHF was associated with a greater degree of hypertrophy. Ventricular performance, as assessed in an isovolumic heart apparatus, was markedly depressed in both infarct groups with CHF and was not affected by Db. Db increased myosin ATPase activity in control and infarcted animals both with and without congestive heart failure. Myosin oxygen consumption and lactate production were not adversely affected by Db.

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Greenberg, Michael J., Tanya R. Mealy, James D. Watt, Michelle Jones, Danuta Szczesna-Cordary, and Jeffrey R. Moore. "The molecular effects of skeletal muscle myosin regulatory light chain phosphorylation." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 297, no. 2 (August 2009): R265—R274. http://dx.doi.org/10.1152/ajpregu.00171.2009.

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Phosphorylation of the myosin regulatory light chain (RLC) in skeletal muscle has been proposed to act as a molecular memory of recent activation by increasing the rate of force development, ATPase activity, and isometric force at submaximal activation in fibers. It has been proposed that these effects stem from phosphorylation-induced movement of myosin heads away from the thick filament backbone. In this study, we examined the molecular effects of skeletal muscle myosin RLC phosphorylation using in vitro motility assays. We showed that, independently of the thick filament backbone, the velocity of skeletal muscle myosin is decreased upon phosphorylation due to an increase in the myosin duty cycle. Furthermore, we did not observe a phosphorylation-dependent shift in calcium sensitivity in the absence of the myosin thick filament. These data suggest that phosphorylation-induced movement of myosin heads away from the thick filament backbone explains only part of the observed phosphorylation-induced changes in myosin mechanics. Last, we showed that the duty cycle of skeletal muscle myosin is strain dependent, consistent with the notion that strain slows the rate of ADP release in striated muscle.

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Toyoshima, N., N. Hirakawa, Y. Kimura, K. Okamoto, A. Ishijima, and S. Fujime. "Mechanics of Chara myosin measured by an optical tweezers." Seibutsu Butsuri 40, supplement (2000): S199. http://dx.doi.org/10.2142/biophys.40.s199_4.

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31

Redaelli, A., M. Soncini, and F. M. Montevecchi. "Myosin cross-bridge mechanics: geometrical determinants for continuous sliding." Journal of Biomechanics 34, no. 12 (December 2001): 1607–17. http://dx.doi.org/10.1016/s0021-9290(01)00140-3.

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32

Finer, Jeffrey T., Robert M. Simmons, and James A. Spudich. "Single myosin molecule mechanics: piconewton forces and nanometre steps." Nature 368, no. 6467 (March 1994): 113–19. http://dx.doi.org/10.1038/368113a0.

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33

Lecarpentier, Y., F. X. Blanc, J. Quillard, J. L. Hébert, X. Krokidis, and C. Coirault. "Statistical mechanics of myosin molecular motors in skeletal muscles." Journal of Theoretical Biology 235, no. 3 (August 2005): 381–92. http://dx.doi.org/10.1016/j.jtbi.2005.01.018.

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34

Cai, Shuang, Lidija Pestic-Dragovich, Martha E. O’Donnell, Ning Wang, Donald Ingber, Elliot Elson, and Primal De Lanerolle. "Regulation of cytoskeletal mechanics and cell growth by myosin light chain phosphorylation." American Journal of Physiology-Cell Physiology 275, no. 5 (November 1, 1998): C1349—C1356. http://dx.doi.org/10.1152/ajpcell.1998.275.5.c1349.

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The role of myosin light chain phosphorylation in regulating the mechanical properties of the cytoskeleton was studied in NIH/3T3 fibroblasts expressing a truncated, constitutively active form of smooth muscle myosin light chain kinase (tMK). Cytoskeletal stiffness determined by quantifying the force required to indent the apical surface of adherent cells showed that stiffness was increased twofold in tMK cells compared with control cells expressing the empty plasmid (Neo cells). Cytoskeletal stiffness quantified using magnetic twisting cytometry showed an ∼1.5-fold increase in stiffness in tMK cells compared with Neo cells. Electronic volume measurements on cells in suspension revealed that tMK cells had a smaller volume and are more resistant to osmotic swelling than Neo cells. tMK cells also have smaller nuclei, and activation of mitogen-activated protein kinase (MAP kinase) and translocation of MAP kinase to the nucleus are slower in tMK cells than in control cells. In tMK cells, there is also less bromodeoxyuridine incorporation, and the doubling time is increased. These data demonstrate that increased myosin light chain phosphorylation correlates with increased cytoskeletal stiffness and suggest that changing the mechanical characteristics of the cytoskeleton alters the intracellular signaling pathways that regulate cell growth and division.

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35

Ma, Weikang, Marcus Henze, Robert L. Anderson, Henry Gong, Fiona L. Wong, Carlos L. del Rio, and Thomas Irving. "The Super-Relaxed State and Length Dependent Activation in Porcine Myocardium." Circulation Research 129, no. 6 (September 3, 2021): 617–30. http://dx.doi.org/10.1161/circresaha.120.318647.

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Rationale: Myofilament length-dependent activation (LDA) is the key underlying mechanism of cardiac heterometric autoregulation, commonly referred as the Frank-Starling Law of the heart. Although alterations in LDA are common in cardiomyopathic states, the precise structural and biochemical mechanisms underlying LDA remain unknown. Objective: Here, we examine the role of structural changes in the thick filament during diastole, in particular changes in the availability of myosin heads, in determining both calcium sensitivity and maximum contractile force during systole in permeabilized porcine cardiac fibers. Methods and Results: Permeabilized porcine fibers from ventricular myocardium were studied under relaxing conditions at short and long sarcomere length using muscle mechanics, biochemical measurements, and X-ray diffraction. Upon stretch, the porcine myocardium showed the increased calcium sensitivity and maximum calcium-activated force characteristic of LDA. Stretch increased diastolic ATP turnover, recruiting reserve myosin heads from the super-relaxed state at longer sarcomere length. Structurally, X-ray diffraction studies in the relaxed-muscle confirmed a departure from the helical ordering of the thick filament upon stretch which occurred concomitantly with a displacement of myosin heads towards actin, facilitating cross-bridge formation upon systolic activation. Mavacamten, a selective myosin-motor inhibitor known to weaken the transition to actin-bound power-generating states and to enrich the ordered super-relaxed state myosin population, reversed the structural effects of stretch on the thick filament, blunting the mechanical consequences of stretch; mavacamten did not, however, prevent other structural changes associated with LDA in the sarcomere, such as decreased lattice spacing or troponin-displacement. Conclusions: Our findings strongly indicate that in ventricular muscle, LDA and its systolic consequences are dependent on the population of myosin heads competent to form cross bridges and involves the recruitment of myosin heads from the reserve super-relaxed state pool during diastole.

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Egan, Paul F., Jeffrey R. Moore, Allen J. Ehrlicher, David A. Weitz, Christian Schunn, Jonathan Cagan, and Philip LeDuc. "Robust mechanobiological behavior emerges in heterogeneous myosin systems." Proceedings of the National Academy of Sciences 114, no. 39 (September 12, 2017): E8147—E8154. http://dx.doi.org/10.1073/pnas.1713219114.

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Biological complexity presents challenges for understanding natural phenomenon and engineering new technologies, particularly in systems with molecular heterogeneity. Such complexity is present in myosin motor protein systems, and computational modeling is essential for determining how collective myosin interactions produce emergent system behavior. We develop a computational approach for altering myosin isoform parameters and their collective organization, and support predictions with in vitro experiments of motility assays with α-actinins as molecular force sensors. The computational approach models variations in single myosin molecular structure, system organization, and force stimuli to predict system behavior for filament velocity, energy consumption, and robustness. Robustness is the range of forces where a filament is expected to have continuous velocity and depends on used myosin system energy. Myosin systems are shown to have highly nonlinear behavior across force conditions that may be exploited at a systems level by combining slow and fast myosin isoforms heterogeneously. Results suggest some heterogeneous systems have lower energy use near stall conditions and greater energy consumption when unloaded, therefore promoting robustness. These heterogeneous system capabilities are unique in comparison with homogenous systems and potentially advantageous for high performance bionanotechnologies. Findings open doors at the intersections of mechanics and biology, particularly for understanding and treating myosin-related diseases and developing approaches for motor molecule-based technologies.

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37

Cooke, R. "Actomyosin interaction in striated muscle." Physiological Reviews 77, no. 3 (July 1, 1997): 671–97. http://dx.doi.org/10.1152/physrev.1997.77.3.671.

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The mechanics of the actomyosin interaction have been extensively studied using the organized filament array of striated muscle. However, the extrapolation of these data to the events occurring at the level of a single actomyosin interaction has not been simple. Problems arise in part because an active fiber has an ensemble of myosin heads that are spread out through the various steps of the active cycle, and it is likely that only a small fraction of the heads are generating tension at any given time. More recently, two new approaches have greatly extended our knowledge of the actomyosin interaction. First, the three-dimensional crystal structures of both the actin monomer and the myosin head have been determined, and these structures have been fit to lower resolution images to give atomic models of the actin filament and of the actin filament decorated by myosin heads. Second, the technology to measure picoNewton forces and nanometer distances has provided direct determinations of the force and step length generated by a single myosin molecule interacting with a single actin filament. This review synthesizes the existing mechanical data obtained from the more-organized array of the muscle filament with the results obtained by these two technologies.

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Toepfer, Christopher N., Markus B. Sikkel, Valentina Caorsi, Anupama Vydyanath, Iratxe Torre, O'Neal Copeland, Alexander R. Lyon, et al. "A post-MI power struggle: adaptations in cardiac power occur at the sarcomere level alongside MyBP-C and RLC phosphorylation." American Journal of Physiology-Heart and Circulatory Physiology 311, no. 2 (August 1, 2016): H465—H475. http://dx.doi.org/10.1152/ajpheart.00899.2015.

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Myocardial remodeling in response to chronic myocardial infarction (CMI) progresses through two phases, hypertrophic “compensation” and congestive “decompensation.” Nothing is known about the ability of uninfarcted myocardium to produce force, velocity, and power during these clinical phases, even though adaptation in these regions likely drives progression of compensation. We hypothesized that enhanced cross-bridge-level contractility underlies mechanical compensation and is controlled in part by changes in the phosphorylation states of myosin regulatory proteins. We induced CMI in rats by left anterior descending coronary artery ligation. We then measured mechanical performance in permeabilized ventricular trabecula taken distant from the infarct zone and assayed myosin regulatory protein phosphorylation in each individual trabecula. During full activation, the compensated myocardium produced twice as much power and 31% greater isometric force compared with noninfarcted controls. Isometric force during submaximal activations was raised >2.4-fold, while power was 2-fold greater. Electron and confocal microscopy demonstrated that these mechanical changes were not a result of increased density of contractile protein and therefore not an effect of tissue hypertrophy. Hence, sarcomere-level contractile adaptations are key determinants of enhanced trabecular mechanics and of the overall cardiac compensatory response. Phosphorylation of myosin regulatory light chain (RLC) increased and remained elevated post-MI, while phosphorylation of myosin binding protein-C (MyBP-C) was initially depressed but then increased as the hearts became decompensated. These sensitivities to CMI are in accordance with phosphorylation-dependent regulatory roles for RLC and MyBP-C in crossbridge function and with compensatory adaptation in force and power that we observed in post-CMI trabeculae.

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Verkhovsky, A. B., T. M. Svitkina, and G. G. Borisy. "Polarity sorting of actin filaments in cytochalasin-treated fibroblasts." Journal of Cell Science 110, no. 15 (August 1, 1997): 1693–704. http://dx.doi.org/10.1242/jcs.110.15.1693.

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The polarity of actin filaments is fundamental for the subcellular mechanics of actin-myosin interaction; however, little is known about how actin filaments are oriented with respect to myosin in non-muscle cells and how actin polarity organization is established and maintained. Here we approach these questions by investigating changes in the organization and polarity of actin relative to myosin II during actin filament translocation. Actin and myosin II reorganization was followed both kinetically, using microinjected fluorescent analogs of actin and myosin, and ultrastructurally, using myosin S1 decoration and immunogold labelling, in cultured fibroblasts that were induced to contract by treatment with cytochalasin D. We observed rapid (within 15 minutes) formation of ordered actin filament arrays: short tapered bundles and aster-like assemblies, in which filaments had uniform polarity with their barbed ends oriented toward the aggregate of myosin II at the base of a bundle or in the center of an aster. The resulting asters further interacted with each other and aggregated into bigger asters. The arrangement of actin in asters was in sharp contrast to the mixed polarity of actin filaments relative to myosin in non-treated cells. At the edge of the cell, actin filaments became oriented with their barbed ends toward the cell center; that is, the orientation was opposite to what was observed at the edge of nontreated cells. This rearrangement is indicative of relative translocation of actin and myosin II and of the ability of myosin II to sort actin filaments with respect to their polarity during translocation. The results suggest that the myosin II-actin system of non-muscle cells is organized as a dynamic network where actin filament arrangement is defined in the course of its interaction with myosin II.

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Weirich, Kimberly L., Samantha Stam, Edwin Munro, and Margaret L. Gardel. "Actin bundle architecture and mechanics regulate myosin II force generation." Biophysical Journal 120, no. 10 (May 2021): 1957–70. http://dx.doi.org/10.1016/j.bpj.2021.03.026.

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41

Shirai, K., H. Machiyama, and A. Ishijima. "Single molecule mechanics of Chara myosin : to keep motile activity." Seibutsu Butsuri 43, supplement (2003): S145. http://dx.doi.org/10.2142/biophys.43.s145_2.

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42

Nose, H., H. Machiyama, and A. Ishijima. "3P167 Single molecule mechanics of Chara myosin : investigation of processivity." Seibutsu Butsuri 44, supplement (2004): S231. http://dx.doi.org/10.2142/biophys.44.s231_3.

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43

Kojima, H., K. Ito, S. Kimura, K. Yamamoto, and K. Oiwa. "1P169 Single molecule mechanics of recombinant Chara myosin motor domain." Seibutsu Butsuri 45, supplement (2005): S74. http://dx.doi.org/10.2142/biophys.45.s74_1.

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44

Duno-Miranda, Sebastian, Shane R. Nelson, David Rasicci, Skylar M. L. Bodt, Duha Vang, Sivaraj Sivaramakrishnan, Christopher M. Yengo, and David M. Warshaw. "Molecular mechanics of E525K dilated cardiomyopathy mutant human cardiac myosin." Biophysical Journal 122, no. 3 (February 2023): 406a. http://dx.doi.org/10.1016/j.bpj.2022.11.2206.

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45

Hai, Chi-Ming, and Hak Rim Kim. "An expanded latch-bridge model of protein kinase C-mediated smooth muscle contraction." Journal of Applied Physiology 98, no. 4 (April 2005): 1356–65. http://dx.doi.org/10.1152/japplphysiol.00834.2004.

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A thin-filament-regulated latch-bridge model of smooth muscle contraction is proposed to integrate thin-filament-based inhibition of actomyosin ATPase activity with myosin phosphorylation in the regulation of smooth muscle mechanics. The model included two latch-bridge cycles, one of which was identical to the four-state model as proposed by Hai and Murphy ( Am J Physiol Cell Physiol 255: C86–C94, 1988), whereas the ultraslow cross-bridge cycle has lower cross-bridge cycling rates. The model-fitted phorbol ester induced slow contractions at constant myosin phosphorylation and predicted steeper dependence of force on myosin phosphorylation in phorbol ester-stimulated smooth muscle. By shifting cross bridges between the two latch-bridge cycles, the model predicts that a smooth muscle cell can either maintain force at extremely low-energy cost or change its contractile state rapidly, if necessary. Depending on the fraction of cross bridges engaged in the ultraslow latch-bridge cycle, the model predicted biphasic kinetics of smooth muscle mechanics and variable steady-state dependencies of force and shortening velocity on myosin phosphorylation. These results suggest that thin-filament-based regulatory proteins may function as tuners of actomyosin ATPase activity, thus allowing a smooth muscle cell to have two discrete cross-bridge cycles with different cross-bridge cycling rates.

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46

Greene, Peter R. "Effects of Thermal Tension Transients on the Muscle Crossbridge." Biophysical Reviews and Letters 11, no. 03 (September 2016): 117–26. http://dx.doi.org/10.1142/s1793048016500053.

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The transverse thermal fluctuations of the myosin molecule are significant. This paper explores the contribution of lateral myosin bending to the developed crossbridge force and power stroke. The equipartition theorem is used to calculate the mode amplitudes for myosin bending. Crossbridge axial force [Formula: see text] and power stroke [Formula: see text] are developed by transverse in-plane fluctuations along the [Formula: see text]- and [Formula: see text]-axes. Practical applications include the effects of temperature on the flexibility of the myosin molecule stiffness and tension, relevant to man-made fabrication of synthetic muscle using micromachines and nanowires. Scaling laws for the [Formula: see text] bending amplitude depend on filament length, mode number, and stiffness, as [Formula: see text], and (EI)[Formula: see text]. This paper quantifies the effects of thermal motion on the mechanics of miniature molecular motors, including the muscle crossbridge.

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Pérez-Domínguez, Sandra, Javier López-Alonso, Frank Lafont, and Manfred Radmacher. "Comparison of Rheological Properties of Healthy versus Dupuytren Fibroblasts When Treated with a Cell Contraction Inhibitor by Atomic Force Microscope." International Journal of Molecular Sciences 24, no. 3 (January 20, 2023): 2043. http://dx.doi.org/10.3390/ijms24032043.

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Mechanical properties of healthy and Dupuytren fibroblasts were investigated by atomic force microscopy (AFM). In addition to standard force curves, rheological properties were assessed using an oscillatory testing methodology, in which the frequency was swept from 1 Hz to 1 kHz, and data were analyzed using the structural damping model. Dupuytren fibroblasts showed larger apparent Young’s modulus values than healthy ones, which is in agreement with previous results. Moreover, cell mechanics were compared before and after ML-7 treatment, which is a myosin light chain kinase inhibitor (MLCK) that reduces myosin activity and hence cell contraction. We employed two different concentrations of ML-7 inhibitor and could observe distinct cell reactions. At 1 µM, healthy and scar fibroblasts did not show measurable changes in stiffness, but Dupuytren fibroblasts displayed a softening and recovery after some time. When increasing ML-7 concentration (3 µM), the majority of cells reacted, Dupuytren fibroblasts were the most susceptible, not being able to recover from the drug and dying. These results suggested that ML-7 is a potent inhibitor for MLCK and that myosin II is essential for cytoskeleton stabilization and cell survival.

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Sonn-Segev, Adar, Anne Bernheim-Groswasser, and Yael Roichman. "Scale dependence of the mechanics of active gels with increasing motor concentration." Soft Matter 13, no. 40 (2017): 7352–59. http://dx.doi.org/10.1039/c7sm01391d.

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We study the effect of myosin concentration on the mechanical properties of actomyosin networks in steady state. We find that the fluctuations of tracer particles embedded in the network decrease in amplitude as motor concentration increases, while the networks' stiffness increases.

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Samson, Shiela C., Andrew Elliott, Brian D. Mueller, Yung Kim, Keith R. Carney, Jared P. Bergman, John Blenis, and Michelle C. Mendoza. "p90 ribosomal S6 kinase (RSK) phosphorylates myosin phosphatase and thereby controls edge dynamics during cell migration." Journal of Biological Chemistry 294, no. 28 (May 28, 2019): 10846–62. http://dx.doi.org/10.1074/jbc.ra119.007431.

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Cell migration is essential to embryonic development, wound healing, and cancer cell dissemination. Cells move via leading-edge protrusion, substrate adhesion, and retraction of the cell's rear. The molecular mechanisms by which extracellular cues signal to the actomyosin cytoskeleton to control these motility mechanics are poorly understood. The growth factor-responsive and oncogenically activated protein extracellular signal-regulated kinase (ERK) promotes motility by signaling in actin polymerization-mediated edge protrusion. Using a combination of immunoblotting, co-immunoprecipitation, and myosin-binding experiments and cell migration assays, we show here that ERK also signals to the contractile machinery through its substrate, p90 ribosomal S6 kinase (RSK). We probed the signaling and migration dynamics of multiple mammalian cell lines and found that RSK phosphorylates myosin phosphatase–targeting subunit 1 (MYPT1) at Ser-507, which promotes an interaction of Rho kinase (ROCK) with MYPT1 and inhibits myosin targeting. We find that by inhibiting the myosin phosphatase, ERK and RSK promote myosin II–mediated tension for lamella expansion and optimal edge dynamics for cell migration. These findings suggest that ERK activity can coordinately amplify both protrusive and contractile forces for optimal cell motility.

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Lecarpentier, Edouard R., Victor A. Claes, Oumar Timbely, Abdelilah Arsalane, Jacques A. Wipff, Jean-Louis M. Hébert, Francine Y. Michel, and Yves C. Lecarpentier. "Mechanics and energetics of myosin molecular motors from nonpregnant human myometrium." Journal of Applied Physiology 111, no. 4 (October 2011): 1096–105. http://dx.doi.org/10.1152/japplphysiol.00414.2011.

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Mechanical properties of spontaneously contracting isolated nonpregnant human myometrium (NPHM) were investigated throughout the whole continuum of load from zero load up to isometry. This made it possible to assess the three-dimensional tension-velocity-length (T-V-L) relationship characterizing the level of contractility and to determine crossbridge (CB) kinetics of myosin molecular motors. Seventy-seven muscle strips were obtained from hysterectomy in 42 nonpregnant patients. Contraction and relaxation parameters were measured during spontaneous mechanical activity. The isotonic tension-peak velocity (T-V) relationship was hyperbolic in 30 cases and nonhyperbolic in 47 cases. When the T-V relationship was hyperbolic, the Huxley formalism could be used to calculate CB kinetics and CB unitary force. At the whole muscle level and for a given isotonic load level, part of the V-L phase plane showed a common pathway, so that a given instantaneous length corresponded to only one possible instantaneous velocity, independent of time and initial length. At the molecular level, rate constants for CB attachment and detachment were dramatically low, ∼100 times lower than those of striated muscles, and ∼5 to 10 times lower than those of other smooth muscles. The CB unitary force was ∼1.4 ± 0.1 pN. NPHM shared similar basic contractile properties with striated muscles, reflected in the three-dimensional T-V-L relationship characterizing the contractile level. Low CB attachment and detachment rate constants made it possible to generate normal CB unitary force and normal muscle tension in NPHM, even though it contracted extremely slowly compared with other muscles.

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Journal articles on the topic 'Myosin mechanics'

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