Heavy meromyosin
Heavy meromyosin (HMM) is the larger of the two fragments obtained from the muscle protein myosin II following limited proteolysis by trypsin or chymotrypsin.[2] The Heavy Meromyosin fragment holds a critical funtion, as it is responsible for regulation ATPase enzymatic activity and mediating the binding interaction with actin filaments.[3]HMM contains two domains S-1 and S-2, which can be cleaved apart by papain. S-1 contains the globular head that can bind to actin, while the S-2 domain projects at an angle from light meromyosin (LMM), connecting the two meromyosin fragments.[2]
ATPase Regulation
[edit]Heavy meromyosin increase drastically its activity when it attaches to actin filaments fil. It's ATPase activity can intensify several times because the S1 heads hydrolyze adenosine triphosphate (ATP) in a cycle where binding the acting speeds up phosphate release and force generation.[4] In some organism, calcium ions (Ca²+) bind directly to HMM and increase the maximum rate (Vmax) of ATPase catalytic activity. This happens because calcium changes the steps that occur after binding, not just the affinity between molecules. When calcium levels are low, some steps of ATP hydrolysis become slower.[4][5]
Applications of Heavy Meromyosin
[edit]HMM is used to determine the polarity of actin filaments by decorating them with HMM then viewing them under the electron microscope.[6]
References
[edit]- ↑ Reconditi, Massimo (1 October 2006). "RECENT IMPROVEMENTS IN SMALL ANGLE X-RAY DIFFRACTION FOR THE STUDY OF MUSCLE PHYSIOLOGY". Reports on Progress in Physics. Physical Society (Great Britain). 69 (10): 2709–2759. doi:10.1088/0034-4885/69/10/R01. ISSN 1361-6633. PMC 2783642. PMID 19946470.
- 1 2 Sellers, J. R. (1985). "Mechanism of the phosphorylation-dependent regulation of smooth muscle heavy meromyosin". The Journal of Biological Chemistry. 260 (29): 15815–15819. doi:10.1016/S0021-9258(17)36331-7. PMID 2933403.
- ↑ Rastogi, Khushboo; Puliyakodan, Mohammed Shabeel; Pandey, Vikas; Nath, Sunil; Elangovan, Ravikrishnan (24 August 2016). "Maximum limit to the number of myosin II motors participating in processive sliding of actin". Scientific Reports. 6 (1) 32043. doi:10.1038/srep32043. ISSN 2045-2322. PMC 4995457.
- 1 2 Wagner, P. D.; Giniger, E. (25 December 1981). "Calcium-sensitive binding of heavy meromyosin to regulated actin in the presence of ATP". The Journal of Biological Chemistry. 256 (24): 12647–12650. ISSN 0021-9258. PMID 6458606.
- ↑ Stafford, W. F; Jacobsen, M. P; Woodhead, J; Craig, R; O'Neall-Hennessey, E; Szent-Györgyi, A. G (16 March 2001). "Calcium-dependent structural changes in scallop heavy meromyosin1". Journal of Molecular Biology. 307 (1): 137–147. doi:10.1006/jmbi.2000.4490. ISSN 0022-2836.
- ↑ Woodrum, D. T.; Rich, S. A.; Pollard, T. D. (1975). "Evidence for biased bidirectional polymerization of actin filaments using heavy meromyosin prepared by an improved method". Journal of Cell Biology. 67 (1): 231–237. doi:10.1083/jcb.67.1.231. PMC 2109590. PMID 240859.
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