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Myosin II

Updated 21/5/02

The classic myosin first isolated from muscle, subsequently found in non-muscle cells and protists (Adelman & Taylor, 1969).  It is now clear that there are likely to be no myosin II members expressed in plants as there is none in the complete genome of Arabidopsis thaliana (Reddy et al, 2001).
Figure 1. The myosin II molecule is composed of two heavy chains and two sets of light chains.  The light chains are the Essential Light Chains (ELC) and Regulatory Light Chains (RLC). Overall activity and polymerization can be modulated by phosphorylation on the light chains and the C-terminus of the heavy chains respectively.
The role of myosin II in muscle contraction.
Myosin II provides the motive force behind the contraction of muscle cells, working in concert with the actin filaments.  The sliding filament theory first suggested by Hugh Huxley (
Huxley & Hanson, 1954) is now widely accepted.  However the details are still hotly debated.  
Figure 2a.  An electron microscope image of rat skeletal muscle showing the characteristic organisation of the sarcomere.  With two prominent Z-discs, a "thick" filament composed of myosin and two sets of ""thin filaments composed largely of actin. 
2b.  A diagram showing the main components of the sarcromere.  Thick filaments in blue, thin filaments in red.  Note that the thick filament is held between the thin filaments by "Titin" - an enormous spring-like molecule with many site for other muscle proteins including actin (See Titin at the Z disc for more info). The Z- disc to Z-disc distance is about 2.5mm depending of course on the state of contractility.

 

Figure 3a.  The Myosin Cross-bridge Cycle.  A.  ATP binding to a cleft at the “back” of the head causes a conformation which cannot bind actin.  B.  As the ATP is hydrolysed, the head swings back about 5nm to the “cocked” position the ADP and Pi remain bound.  C+D.  The force generating stages.  When the Pi leaves the myosin, the head binds the actin and the “power stroke” is released as the head bind actin.  ADP is released to continue the cycle.  At this stage the head in bound to actin in the “rigor” or tightly bound state.
The role of myosin II in cell locomotion.

Cell locomotion has been studied for more than a century.  The earliest work involved the giant amoeba (Amoeba, Chaos) and two competing hypothesis, the frontal contraction hypothesis and the rear contraction hypothesis (Janson  & Taylor, 1993). The discovery of myosin II in protists encouraged suggestions of its involvement in the production of contraction (either at the from or rear of the amoeba cortex), however, it was shown that the deletion of the single myosin II gene from Dictyostelium discoideum did not destroy its ability to crawl (although it did cause the amoeba to move in a less organised fashion)(Knecht & Loomis 1987). (See Cell Locomotion and Myosin & Cell locomotion for further details).  

 

References:-

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Hammer III, J. A., Korn, E. D. & Paterson, B. M. (1986) Isolation of a non-muscle myosin heavy chain gene from Acanthamoeba., J.Biol.Chem. 261, 1949-1956.

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Höner, B., Citi, S., Kendrick-Jones, J. & Jockusch, B. M. (1988) Modulation of cellular morphogenesis and locomotory activity by antibodies against myosin, J.Cell Biol. 107, 2181-2189.

Huxley, H. E. & Hanson, J. (1954) Changes in the cross-striations of muscle contractions and their structural interpretation. Nature. 173, 973-977.

Ishijima, A., Kojima, H., Funatsu, T., Tokunaga, M., Higuchi, H., Tanaka, H. & Yanagida, T. (1998) Simultaneous observation of individual ATPase and mechanical events by a single myosin molecule during interaction with actin, Cell. 92, 161-171.

Janson, L. W. & Taylor, D. L. (1993) In vitro models of tail contraction and cytoplasmic streaming in amoeboid cells, J. Cell Biol. 123, 345-356.

Katoh, K., Kano, Y., Amano, M., Onishi, H., Kaibuchi, K. & Fujiwara, K. (2001) Rho-kinase-mediated contraction of isolated stress fibers., J. Cell Biol. 153, 569-583.

Knecht, D. A. & Loomis, W. F. (1987) Antisense RNA inactivation of myosin heavy chain gene expression in Dictyostelium discoideum., Science. 236, 1081-1085.

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 Labbé, J. P., Boyer, M., Méjean, C., Roustan, C. & Benyamin, Y. (1993) Localization of two myosin-subfragment-1 binding contacts in the 96-132 region of actin subdomain-1., Eur.J.Biochem. 215, 17-24.

Langanger, G., Moeremans, M., Daneels, G., Sobieszek, A., De Brabander, M. & De Mey, J. (1986) The molecular organization of myosin in stress fibres of cultured cells, J.Cell Biol. 102, 200-209.

Lippincott, J. & Li, R. (1998) Sequential assembly of myosin II, an IQGAP-like protein, and filamentous actin to a ring structure involved in budding yeast cytokinesis, J.Cell Biol. 140, 355-366.

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Matsumura, F., Ono, S., Yamakita, Y., Totsukawa, G. & Yamashiro, S. (1998) Specific localization of serine 19 phosphorylated myosin II during cell locomotion and mitosis of cultured cells., J.Cell Biol. 140, 119-129.

May, K. M., Win, T. Z. & Hyams, J. S. (1998) Yeast myosin II: A new subclass of unconventional conventional myosins?, Cell Mot.Cytoskeleton. 39, 195-200.

Medeiros, N. A., Reese, T. S., Jaffe, H., Degiorgis, J. A. & Bearer, E. L. (1998) Primary peptide sequence from squid muscle and optic lobe myosin IIs: A strategy to identify an organelle myosin., Cell Biol.Internat. 22, 161-173.

Moores, S. L. & Spudich, J. A. (1998) Conditional loss-of-myosin-II-function mutants reveals a position in the tail that is critical for filament formation., Mol.Cell. 1, 1043-1050.

Murata, K., Hirano, K., Villa-Moruzzi, E., Hartshorne, D. J. & Brautigan, D. L. (1997) Differential localization of myosin and myosin phosphatase subunits in smooth muscle cells and migrating fibroblasts, Mol.Cell Biol. 8, 663-673.

Neujahr, R., Heizer, C. & Gerisch, G. (1997) Myosin II-independent processes in mitotic cells of Dictyostelium discoideum: redistribution of the nuclei, re-arrangement of the actin system and formation of the cleavage furrow., J.Cell Sci. 110, 123-137.

Pasternak, C., Spudich, J. A. & Elson, E. L. (1989) Capping of surface receptors and concomitant cortical tension are generated by conventional myosins, Nature. 341, 549-551.

Razzaq, A., Schmitz, S., Veigel, C., Molloy, J. E., Geeves, M. A. & Sparrow, J. C. (1999) Actin residue Glu93 is identified as an amino acid affecting myosin binding., J.Biol.Chem. 274, 28321-28328.

Reddy, A. S. N. & Day, I. S. (2001) Analysis of the myosins encoding in the recently completed Arabidopsis thaliana genome sequence., Genome Biology. 2, 24.1-24.17.

Shu, S., Lee, R. J., LeBlanc-Straceski, J. M. & Uyeda, T. Q. P. (1999) Role of myosin II tail sequence in its function and localization at the cleavage furrow in Dictyostelium., J.Cell Sci. 112, 2195-2201.

Surks, H. K., Mochizuki, N., Kasai, Y., Georgescu, S. P., Tang, K. M., Ito, M., Lincoln, T. M. & Mendelsohn, M. E. (1999) Regulation of myosin phosphatase by a specific interaction with cGMP-dependent protein kinase1a., Science. 286, 1583-1587.

Svitkina, T. M., Verkovsky, A. B., McQuade, K. M. & Borisy, G. G. (1997) Analysis of the actin-myosin II system in fish epidermal keratocytes: Mechanism of cell body translocation., J.Cell Biol. 139, 397-415.

Verkhovsky, A. B., Svitkina, T. M. & Borisy, G. G. (1998) Self-polarization and directional motility of cytoplasm, Curr.Biol. 9, 11-20.

Weber, I., Neujahr, R., Du, A., Kohler, J., Faix, J. & Gerisch, G. (2000) Two-step positioning of a cleavage furrow by cortexillins and myosin II., Current Biology. 10, 501-506.

Wylie, S. R. & Chantler, P. D. (2001) Separate but linked functions of conventional myosins modulate adhesion and neurite outgrowth., Nature Cell Biol. 3, 88-92.

Yanagida, T., Harada, Y. & Ishijama, A. (1993) Nano-manipulation of actomyosin molecular motors in vitro: a new working principle, Trends Biochem. 18, 319-324.

Yumura, S. (2001) Myosin II dynamics and cortical flow during contractile ring formation in Dictyostelium cells., J.Cell Biol. 154, 137-145.

Yumura, S. & Uyeda, T. Q. P. (1997) Myosin II can be localized to the cleavage furrow and to the posterior region of Dictyostelium amoebae without control by phosphorylation of myosin heavy and light chains., Cell Mot.Cytoskel. 36, 313-322.

Zischka, H., Oehme, F., Pintsch, T., Ott, A., Keller, H., Kellermann, J. & Schuster, S. (1999) Rearrangment of cortex proteins constitutes an osmoprotective mechanism in Dictyostelium., EMBO J. 18, 4241-4249.

 

 
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