Meromyosin

Huxley suggested that crossbridges can move out in this way and bind to actin because S-2 of HMM acted as a flexible link between LMM in the thick filament backbone and S-1. This was based on the observation that heavy meromyosin could be digested by chymotrypsin into two further subffagments (Lowey et al., 1966), S-1 and S-2, as described above, and that S-1 contained the ATPase and actin binding sites, whereas S-2 did not moreover, S-2 did not self-aggregate, as did the rod or LMM portion of myosin. 

Eisenberg, E. Moos, C. (1968). Adenosine triphosphate activity of acto-heavy meromyosin A kinetic analysis of actin activation. Biochemistry 7, 1486-1489. 

Lowey, S., Goldstein, L., Cohen, C., Luck, S.M. (1966). Proteolytic degradation of myosin and the meromyosins by a water-insoluble polyanionic derivative of trypsin. J. Mol. Biol. 23,287-304. 

Szent-Gydrgyi, A.G. (1953). Meromyosin, the subunits of myosin. Arch. Biochem. Biophys. 42, 305-320. 

Trentham, D.R., Bardsley, R.G., Eccleston, J.F., Weeds, G. (1972). Elementary processes of the magnesium ion-dependent adenosine triphosphatase activity of heavy meromyosin. Biochem. J. 126, 635-644. 

When myosin is digested with trypsin, two myosin fragments (meromyosins) are generated. L ht mero-myosin (LMM) consists of aggregated, insoluble a-he-hcal fibers from the tail of myosin (Figure 49 ). LMM... 

Heavy meromyosin (HMM molecular mass about 340 kDa) is a soluble protein that has both a fibrous portion and a globular portion (Figure 49-4). It exhibits ATPase activity and binds to F-actin. Digestion of HMM with papain generates two subfragments, S-1 and S-2. The S-2 fragment is fibrous in character, has no ATPase activity, and does not bind to F-actin. 

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.

The two ends of the F-actin filaments have different surfaces of the monomer exposed and grow at different rates. This has been demonstrated by allowing the myosin fragment called heavy meromyosin (HMM see Fig. 19-10) to bind to (or "decorate") an actin filament. The... 

Figure 19-10 (A) An approximate scale drawing of the myosin molecule. The "hinge" is a region that is rapidly attacked by trypsin to yield the light and heavy meromyosins (LMM and HMM). Total length -160 nm, molecular mass, 470 kDa two -200-kDa heavy chains two pairs of 16- to 21-kDa light chains heads -15 x 4 x 3 nm. (B) Electron micrograph of rabbit myosin monomers that became dissociated from thick filaments in the presence of ATP, fixed and shadowed with platinum.127 Courtesy of Tsuyoshi Katoh.

Bennett, P. M. (1981). The structure of spindle-shaped paracrystals of light meromyosin. / Mol. Biol. 146, 201-221. 

Onishi, H., Maeda, K., Maeda, Y., Inoue, A., and Fujiwara, K. (1995). Functional chicken gizzard heavy meromyosin expression in and purification from baculovirus-infected insect cells. Proc. Natl. Acad. Sci. USA 92, 704-708. [Published erratum appears in Proc. Natl. Acad. Sci. USA 1995 92, 3076],... 

Pato, M. D., Sellers, J. R, Preston, Y. A., Harvey, E. V., and Adelstein, R. S. (1996). Baculovirus expression of chicken nonmuscle heavy meromyosin II-B. Characterization of alternatively spliced isoforms./. Biol. Chem. 271, 2689-2695. 

Warshaw, D. M., Guilford, W. H., Freyzon, Y., Krementsova, E., Palmiter, K. A., Tyska, M. J., Baker, J. E., and Trybus, K. M. (2000). The light chain binding domain of expressed smooth muscle heavy meromyosin acts as a mechanical lever./. Biol. Chem. 275, 37167-37172. 

King, G.J. and Holtrop, M.E. (1975) Actin-like filaments in bone cells of cultured mouse calvaria as demonstrated by binding to heavy meromyosin. Journal of Cell Biology 66 445-451... 

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