Myosin heavy and light chains

Kawamoto, S., Bengue,A. R., Sellers,). R., Adelstein, R. S. (1989). In situ phosphorylation of human platelet myosin heavy and light chains by protein kinase C. 

Starr and Offer (1971) examined the SDS—gel electrophoresis patterns of conventional myosin preparations and pointed out the presence of several unknown protein bands other than myosin heavy and light chains. As a result, C (135 kDa), F (121 kDa), and H (74 kDa) proteins have been isolated and shown to be myosin-associated proteins. The C protein, discovered by Offer et al. (1973), is localized to seven regularly spaced stripes in each half of the A bands of rabbit psoas muscle (Craig and Offer, 1976), and studies using monoclonal antibodies have shown... 

On the other hand, it has been suggested, based on immunopre-cipitation reactions, that CCT might interact with a broad range (accounting for 9-15%) of newly synthesized eukaryotic proteins (Feldman and Frydman, 2000 McCallum et al., 2000 Thulasiraman et al., 1999). There is also evidence that some proteins other than actins and tubulins fold via interaction with CCT. These include G -transducin (Farr etal, 1997), cyclinE (Won etal., 1998), and the von Hippel-Landau tumor suppressor protein VHL (Feldman et al., 1999). Moreover, translation in vitro of myosin heavy and light chains has identified an intermediate in the biogenesis of the heavy meromyosin subunit (HMM) of skeletal muscle myosin that contains all three myosin subunits and CCT, from which partially folded HMM can be released in an ATP-dependent reaction. Other as yet unknown cytosolic protein(s) are also apparently required for the completion of the myosin folding reaction (Srikakulam and Winkelmann, 1999). 

Johnson D, Cohen P, Chen MX, Chen YH, Cohen PTW. (1997) Identification of the regions on the Muo subunit of protein phosphatase IM that interact with the M21 subunit and myosin. Eur J Biochem 244 931-939 Juhaszova M, Blaustein MP (1997) Na pump low and high ouabain affinity a subunit isoforms are differently distributed in cells. Proc Natl Acad Sci USA 94 1800-1805 Kamm KE, Hsu L-C, Kubota Y, Stull JT (1989) Phosphorylation of smooth muscle myosin heavy and light chains. J Biol Chem 264 21223-21229... 

Morano I, Erb G, Sogl B Expression of myosin heavy and light chains changes during pregnancy in the rat uterus (1993) Eur J Physiol 1993 423 434-441... 

Gaylinn BD, Eddinger TJ, Martino PA, Monical PL, Hunt DF, Murphy RA (1989) Expression of nonmuscle myosin heavy and light chains in smooth muscle. Am J Physiol 257 (Cell Physiol 26) C997-C1004... 

EgeUioff, T.T., Naismith, T.V. and Brozovich, F.V. (1996). Myosin-based cortical tension in Dictyostelium resolved into heavy and light chain-regulated components./. Muscle Res. Cell Motil. 17, 269-274. 

Myosin II is in the same subfamily as the myosins in muscle thick filaments and it forms large, two-headed myosins with two light chains per heavy chain. Although myosin II is abundantly expressed in brain, little is known about its function in the nervous system. In other nonmuscle cells, myosin II has been implicated in many types of cellular contractility and may serve a similar function in developing neurons. However, myosin II remains abundant in the mature nervous system, where examples of cell contractility are less common. 

Adelstein, R. S. (1993). Phosphorylation of vertebrate nonmuscle and smooth muscle myosin heavy chains and light chains. Mol. Cell Biochem. 127-128, 219-227. 

Figure 14.14 Sci ematic diagram of the myosin molecule, comprising two heavy chains (green) that form a coiled-coil tail with two globular heads and four light chains (gray) of two slightly differing sizes, each one bound to each heavy-chain globular head.

Figure 14.15 Stmcture of the SI fragment of chicken myosin as a Richardson diagram (a) and a space-filling model (b). The two light chains are shown in magenta and yellow. The heavy chain is colored according to three proteolytic fragments produced by trypsin a 25-kDa N-terminal domain (green) a central 50-kDa fragment (red) divided by a cleft into a 50K upper and a 50K lower domain and a 20-kDa C-terminal domain (blue) that links the myosin head to the coiled-coil tail. The 50-kDa and 20-kDa domains both bind actin, while the 25-kDa domain binds ATP. [(b) Courtesy of 1. Rayment.]...

Myosin-II phosphorylation is also an important mechanism for regulating myosin assembly in nonmuscle and smooth muscle cells (Kom and Hammer, 1988). For example, myosin-II ixomAcanthamoeba is more soluble when the heavy chain is phosphorylated compared to the unphosphorylated species. Similarly, phosphorylation of the light chains of vertebrate smooth muscle and nonmuscle myosin-II affects filament formation by these myosins. These myosins undergo a... 

Myosin-I molecules have several IQ sequences on or near the head and have light chains associated with them (Cheney and Mooseker, 1992 Cheney et al., 1993). Frequently, the light chains appear to be calmodulin molecules and some myosin-I molecules can bind three to four molecules of calmodulin at one time. Brush-border and adrenal myosin-I also bind calmodulin. Acanthamoeba myosin-I has a light chain that can be removed, in vitro, without adversely affecting the ATPase activity or the heavy chain phosphorylation (Korn and Hammer, 1988). The role of these calmodulin molecules in regulating myosin-I is complex and poorly understood. One possibility is that the calmodulin molecules dissociate from the heavy chains when calcium binds to the calmodulin, thereby imparting greater flexibility to the head of the myosin-I molecules. 

Figure 4.5. Structure of myosin. Myosin comprises both light and heavy chains. The heavy chains may be cleaved by trypsin to generate light meromyosin (LMM) and heavy mero-myosin (HMM). Papain digestion of HMM yields subfragments SI and S2 each SI fragment contains an ATPase site and an actin-binding site. The light chains modify the activity of the ATPase.

It is a large protein that consists of six polypeptide chains, two identical heavy chains (each 220 kDa) and two pairs of light chains (each -20 kDa). The two heavy chains form a long coiled unit known as the tail, which associates laterally with other myosin molecules to form the thick filament. At one end of the chain are the two globular heads which form the crossbridges. Each head has two domains, one on either side. 

Myosin is quantitatively the most important protein in the myofibrils, representing 65% of the total. It is shaped like a golf club (bottom right). The molecule is a hexamer consisting of two identical heavy chains (2 X 223 kDa) and four light chains (each about 20 kDa). Each of the two heavy chains has a globular head at its amino end, which extends into a tail about 150 nm long in which the two chains are intertwined to form a superhelix. The small subunits are attached in the head area. Myosin is present as a bundle of several hundred stacked molecules in the form of a thick myosin filament. The head portion of the molecule acts as an ATPase, the activity of which is modulated by the small subunits. 

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