Myosin cooperativity

For these reasons the Cooperative Hypothesis seems to be a plausible alternative to the Latch Bridge Hypothesis. Given that computer calculations of the behavior of various hypothetical schemes are now possible, an independent, noninvasive measure of distribution of myosin among the states would be of great use for further understanding of crossbridge kinetics. 

Greene, L.E. (1986) Cooperative binding of myosin subfragment one to regulated acdn as measured by fluoresce changes of troponin 1 modified within different fluorophores./. Biol. Chem. 261, 1279. 

Kalof AN, Tam D, Beatty B, Cooper K (2004) Immunostaining patterns of myoepithelial cells in breast lesions a comparison of CD10 and smooth muscle myosin heavy chain. J Clin Pathol 57 625 629... 

A primary function of the SH3 domains is to form fimctional oligomeric complexes at defined subcellular sites, frequently in cooperation with other modular domains. SH3 domains are foimd in many proteins associated with the cytoskeleton or with the plasma membrane. Examples are the actin binding protein a-spectrin and myosin lb. Furthermore, SH3 interactions are involved in signal transduction in the Ras pathway (see Chapter 9). 

Lehrer, S. S., Golitsina, N. L., and Geeves, M. A. (1997). Actin-tropomyosin activation of myosin subfragment 1 ATPase and thin filament cooperativity. The role of tropomyosin flexibility and end-to-end interactions. Biochemistry 36, 13449-13454. 

Tobacman, L. S., and Butters, C. A. (2000). A new model of cooperative myosin-thin filament binding. / Biol. Chem. 275, 27587-27593. 

Boeda, B., El-Amraoui, A., Bahloul, A., Goodyear, R., Daviet, L., Blanchard, S., Perfettini, L, Path, K.R., Shorte, S., Reiners, J., Houdusse, A., Legrain, P, Wolfrum, U., Richardson, G. and Petit, C. (2002) Myosin Vila, harmonin and cadherin 23, three Usher 1 gene products that cooperate to shape the sensory hair cell bundle. EMBO J. 21, 6689-6699. 

The interpenetrating structure (Fig. 8.9) wherein the mobility originates can be described by the Q surface (discussed above). The long-range periodicity, which is a consequence of such a structural description, is relevant to tmderstand the cooperativity and the requirement of synchronisation of the movement of the individual myosin/actin. The phase/curvature approach to the structure of the muscle cell outlined here not only has a didactic value, but adds a new dimension to the discussion of function mechemisms. 

A FIGURE 20-24 Cooperation of myosin and kinesin at the cell cortex. Microtubules approach the actin-rich cell membrane. Consequently, some cargoes are transported to the cell periphery by kinesin motor proteins on microtubules but complete the journey on microfilaments under the power of myosin motor proteins. 

The two heads of smooth muscle myosin interact cooperatively. Studies with the soluble two-headed HMM fragment clearly demonstrate that, whereas the phosphorylation of the two heads by myosin light chain kinase was random, phosphorylation of both heads was required for the MgATPase activity of either head to be activated by actin (Sellers et al., 1983 Per-sechini and Hartshorne, 1981). This cooperative activation of the two heads, coupled with the random phosphorylation, meant that at 50% phosphorylation (i.e., 1 mol Pj/mol HMM) there was only 25% of the... 

FIGURE 9 A troponinlike model for cooperative caldesmon regulation of the thin filament caldesmon (CaD), tropomyosin (TM), actin (A), and myosin (M). Domain 1 corresponds to the N-terminal region of caldesmon domains 3 and 4b represent C-terminal amino acid residues from 508 to 565 and from 658 to 756, respectively. Caltropin (CaT). Reprinted with permission from J.Biol. Chem. (270). Copyright 1995. The American Society for Biochemistry and Molecular Biology. 

However, after this latency, myosin RLC phosphorylation and stiffness both increase more rapidly than either force or cytosolic concentrations (Fig. 2). Interestingly, the kinetics of myosin RLC phosphorylation are described as a pseudo-first-order rate of 1 s i, showing no evidence of an ordered or cooperative phosphorylation of myosin RLC (Kamm and Stull,... 

The rate of phosphorylation is greater than the estimated rate of dephosphorylation, 0.25 s (Kamm and Stull, 1985b). Measurements of nonphosphory-lated, monophosphorylated, and diphosphorylated forms of myosin in tracheal smooth muscle tissue provide direct evidence that myosin RLC phosphorylation occurs as a random rather than an ordered or cooperative phosphorylation process (Persechini etal., 1986). These results are consistent with biochemical measurements (Sellers et al., 1983 Trybus and Lowey,... 

Both RLC phosphorylation and active stiffness increase more rapidly than isometric force during the initiation of the contraction (Kamm and Stull, 1986). These observations suggest that phosphorylation of myosin RLC allows cross-bridge attachment to actin. The delay in force development may result from cooperative effects of phosphorylation on activation whereby force depends on formation of doubly phos-phorylated myosin (Persechini and Hartshorne, 1981 Sellers et al., 1983) however, other contributions, including a delay in the expression of force through series elastic element in the tissue, cannot be excluded (Aksoyetfl/., 1983). 

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