Myosin binding region structure

Also in the A-band, in the middle of each of the bridge regions, the myosin filaments carry the extra protein originally known as C-protein (now often called myosin-binding protein G MyBP-C Offer et al, 1973), which occurs in two sets of 7 to 9 stripes in the G-zones in each half of the A-band (Fig. 5C Bennett et al, 1986 Sjostrom and Squire, 1977). The structure, interactions, and role of G-protein are discussed in Section IV.C. 

Approximately 500 of the 820 amino acid residues of the myosin head are highly conserved between various species. One conserved region, located approximately at residues 170 to 214, constitutes part of the ATP-binding site. Whereas many ATP-binding proteins and enzymes employ a /3-sheet-a-helix-/3-sheet motif, this region of myosin forms a related a-f3-a structure, beginning with an Arg at (approximately) residue 192. The /3-sheet in this region of all myosins includes the amino acid sequence... 

How does this cycle apply to muscle contraction Myosin molecules self-assemble into thick bipolar structures with the myosin heads protruding at both ends of a bare region in the center (Figure 34.19). Approximately 500 head domains line the surface of each thick filament. These domains are paired in myosin dimers, but the two heads within each dimer act independently. Actin filaments associate with each head-rich region, with the barbed ends of actin toward the Z-line. In the presence of normal levels of ATP, most of the myosin heads are detached from actin. Each head can independently hydrolyze ATP, bind to actin, release Pj, and undergo its power stroke. Because few other heads are... 

During the preparation of C protein. Offer et al. (1973) obtained F protein (121 kDa) as a by-product. Miyahara et al. (1980) characterized F protein and showed its binding to myosin. The H protein (74 kDa) has been purified and its specific location closer to the M line than to the C-protein zone has been shown by Yamamoto (1984). The I protein (50 kDa), which inhibits the ATPase activity of myosin, is localized in the edge regions of the A band, but is easily translocated to near the Z lines in aged myofibrils (Ohashi and Maruyama, 1985). The structural roles of F, H, and I proteins have not yet been clarified. 

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