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Changes in molecular motor myosin explain the difference

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The human heart contracts about 70 times a minute, while the mouse heart contracts more than 300 times. What is the cause of this difference? A new study published in an open access journal on June 10 PLOS BiologyIt is led by Michael Geeves and Mark Wass of the University of Kent, and Leslie Leinwand of the University of Colorado at Boulder.


Myosin is a “molecular motor”, a complex nanomachine that forms the dynamic core of the muscle contraction mechanism, burns the chemical energy of cells in the form of ATP, and forces it quickly and reversibly against actin cables. Gives. By doing so, the ends of the muscle cells are drawn to each other, Muscle contractionIt has long been known that the maximum contractility, called V0, varies as expected between mammals. Small mammals Due to its high metabolic rate, it has a higher V0 than large mammals with a low metabolic rate.

There are multiple types of myosin, which play different roles not only in muscle but in every cell of the body. A striking difference in V0 between species is a muscle-specific form called sarcomere myosin (the V0 value of non-muscle isoforms is rarely seen in interspecies differences). Not surprisingly, the amino acid sequences of these sarcomere myosins vary from species to species. mammalian Difference in V0?

The authors compare 67 mammalian beta-myosin (sarcomea-myosin in slow muscle and heart) sequences and differ in the motor domain, which is the region of the molecule that binds to and burns ATP, V0. Further analysis of two different evolutionary lines of mammals, each containing both large and small species, identified 16 sites on the molecule that were particularly relevant to size differences, regardless of lineage. Humans and rats differed in these nine sites.Later when the author modified the human protein to include rats amino acid At these sites, rat-human chimeric proteins functioned like rat proteins, doubling motility, and showing faster release of waste ADP (the rate-limiting stage of contraction).

Increasing size is a common trend in mammalian evolution and is found in multiple strains, including ourselves. “The changes in V0 we observed with chimeric proteins indicate that changes in these residues are likely to have allowed the heart rate reduction required in large animals evolving from small to large. “The fact that the two strains tested in this study both ran into the same solution of slowing contraction was to change the beta,” said one of the authors, Chloe Johnson. Suggests that there are few molecular options MyosinShrinkage rate. ”


Single-molecule imaging reveals how myosin works and causes muscle contraction


For more information:
Johnson CA, McGreig JE, Jeanfavre ST, Walklate J, Vera CD, Farré M, etc. (2021) Identification of sequence changes in myosin II that regulates muscle contraction rate. PLoS Biology 19 (6): e3001248. doi.org/10.1371/journal.pbio.3001248

Quote: Fast Heart, Slow Heart: Changes in Molecular Motor Myosin Explain the Difference (10 June 2021) https://phys.org/news/2021-06-fast-heart-Molecular Motor Motor-Myosin .html

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Changes in molecular motor myosin explain the difference

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