S-Myosin

Myosin and Actomyosin with the L- and S-Myosins of Schramm and Weber... 

Properties Myosin proper of Szent-Gyorgyi L-myosin Actomyosin (Szent-Gyorgyi) S-myosin... 

The difference in between actomyosin and S-myosin is due not to differences in the expert mental values, but to different extrapolation methods. 

On the Apparent Identity of Szent-Gyorgyi s Myosin Fractions with Those of Dubuisson (Supplemented from Dubuisson, 19B0d)... 

There is no longer any doubt that actomyosin is identical with the S-myosins these actin-containing complexes will always be referred to as actomyosins. General data on these proteins e.g., solubility, viscosity, birefringence, will be entered in the Tables as L-myosin. and actomyosin, but footnotes will be added for data obtained on a and /3 myosins electrophoretic data will be discussed using Dubuisson s nomenclature, though for the sake of clarity actomyosin will be added in parentheses after a-myosin, and L-myosin after /3-myosin. 

Dubuisson, it is true (see Dubuisson and Mathieu, 1950), regards this explanation as insufficient a- and /S-myosins do not appear in extracts which are made without delay after the ATP has first been washed out, but they do appear in the usual amounts when ATP is added immediately. The a- and /3-peaks in extracts of fatigued muscle, on the other hand, cannot be augmented in this way (Table XVII). The difference can, however, be explained by assuming nothing more than a denatura-tion of the actomyosin when the ATP content is low, leading to a loss of dissociability when ATP is again added. (See Section III, 66.)... 

Figure Bl.17.12. Time-resolved visualization of the dissociation of myosin SI from filamentous actin (see also figure Bl.17.6). Shown are selected filament images before and after the release of a nucleotide analogue (AMPPNP) by photolysis (a) before flashing, (b) 20 ms, (c) 30 ms, (d) 80 ms and (e) 2 s after flashing. Note the change in obvious order (as shown by the diffraction insert in (a)) and the total dissociation of the complex in (e). The scale bar represents 35.4 mn. Picture with the courtesy of Academic Press.

Warshaw D M, Hayes E, Gaffney D, Lauzon A-M, Wu J, Kennedy G, Trybus K, Lowey S and Berger C 1998 Myosin conformational states determined by single fluorophore polarization Proc. Natl Acad. Sc/. USA 95 8034-9... 

Repeating Structural Elements Are the Secret of Myosin s Coiled Coils... 

FIGURE 17.21 A drawing of the arrangement of the elastic protein titin in the skeletal mnscle sarcomere. Titin filaments originate at the periphery of the M band and extend along the myosin filaments to the Z lines. These titin filaments produce the passive tension existing in myofibrils that have been stretched so that the thick and thin filaments no longer overlap and cannot interact. (Adapted from Ohtsuki, ., Maruyama, K, and Ebashi,. S ., 1986. Advances ia Protein Chemisti y 38 1—67.)... 

Albert Szent-Gyot yi s Discovery of the Effects of Actin on Myosin... 

Szent-Gyorgyi further showed that the viscosity of an actomyosin solution was lowered by the addition of ATP, indicating that ATP decreases myosin s affinity for actin. Kinetic studies demonstrated that myosin ATPase activity was increased substantially by actin. (For this reason, Szent-Gyorgyi gave the name actin to the thin filament protein.) The ATPase turnover number of pure myosin is 0.05/sec. In the presence of actin, however, the turnover number increases to about 10/sec, a number more like that of intact muscle fibers. 

Myosin Subftagment-I Interacts With Two G-Actin Molecules Oligomers of G-Actin and S] Are the Second Intennediates in F-Actin-Si Assembly Conclusion... 

The myosin head has long been shown to induce, even in low ionic strength buffers, polymerization of G-actin into decorated F-actin-S i filaments that exhibit the classical arrowhead structure (Miller et al., 1988 and older references therein). However, to date, the molecular mechanism of this polymerization process remains unknown. 

In an effort to understand how actin-actin interactions might be affected by the binding of the myosin head, and in order to gain more insight into the nature of the actin-myosin interface, we have investigated the nature of the kinetic actin-myosin intermediates involved in the process of S)-induced polymerization of G-actin. For this purpose, a variety of fluorescent probes (e.g., pyrene, NBD, AEDANS) have been covalently attached to the C-terminus of G-actin to probe the G-actin-S] interaction under conditions of tightest binding, i.e., in the absence of ATP. 

Fievez, S. Carlier, M.-F. (1993). Conformational changes in subdomain-2 of G-actin upon polymerization into F-actin and upon binding myosin subfragment-1. FEES Lett. 316, 186-190. 

Doberstein, S.K., Baines, I.C., Wiegand, G., Kom, E.D., Pollard, T.D. (1993). Inhibition of contractile vacuole function in vivo by antibodies against myosin-I. Nature 365, 841-843. 

Geisterfer-Lowrance, A.A., Kass, S., Tanigawa, G., Vosberg, H.-P., McKenna, W., Seidman, C.E., Seidman, J.G. (1990). A molecular basis for familial hypertrophic cardiomyopathy a p-cardiac myosin heavy chain gene missense mutation. Cell 62, 999-1006,... 

Kawamoto, S. Adelstein, R.S. (1987), Characterization of myosin heavy chains in cultured aorta smooth muscle cells. A comparative study. J. Biol. Chem. 262, 7282-7288. 

Trybus, K.M., Huiatt, T.W., Lowey, S. (1982). A bent monomeric conformation of myosin from smooth muscle. Proc. Natl. Acad. Sci. USA 79,6151-6155. 

Adelstein, R.S. Eisenberg, E. (1980). Regulation and kinetics of the actin-myosin-ATP interaction. Ann. Rev. Biochem. 49,921-956. 

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

Lillie, S.H., Brown, S.S. (1992). Suppression of a myosin defect by a kinsein-related gene. Nature 356, 358-361. 

First, in the striated muscles, the cross-sectional organization of filaments is highly ordered in a hexagonal pattern commensurate with the ratio of actin to myosin filaments and the distribution of active myosin heads, S-1 segments, helically every 60 degrees around the myosin filament. In smooth muscle, with perhaps 13 actin filaments per myosin filament, many actin filaments appear to be ranked in layers around myosin filaments. It is not known how the more distant actin filaments participate in contraction. 

The superstructure of smooth muscle actin filaments is differentiated from those of striated muscle by the absence of the troponins and the lateral organization by association of the filaments with dense bodies instead of with the Z-line. How these differences are encoded is again not at all clear. However, the myofibrillar structure and the alignment of the alternating actin and myosin filaments is apparently due primarily to dense bodies and the actin-actinin macrostructures. As the bent dumbbell shaped actins assemble into filaments they are all oriented in the same direction. The S-1 fragments of myosin will bind to actin filaments in vitro and in... 

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