Tropomyosin

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According to B. Alberts[1] tropomyosin is an elongated protein, which stabilizes actin filaments by binding to seven adjacent actin subunits, thus preventing it from interacting with other proteins [2]. Tropomyosin has a coiled coil structure caused by the joining of two alpha helical monomers [3]. Tropomyosin, along with troponin play an important role in regulation of muscle contraction [4]. As tropomyosin binds to actin it follows its helical structure [5]. Fig.1

Accessory proteins troponin and tropomyosin on the actin filament[6]

This figure describes the relative position of accesory proteins and actin in a thin filament. Troponin complex is bound to actin and tropomyosin, which lies in the groove of the actin helix.

Contraction

When a muscle is relaxed, tropomyosin is blocking the myosin binding sites on the thin filament. During the process of contraction, Ca2+ molecules bind to the C-subunit on Troponin which causes the molecule to change its structure, this then pulls away from the myosin binding site and brings tropomyosin a long with it. This then reveals the binding site and allows for the binding of myosin to the thin filament and the beginning of contraction.

References

  1. B. Alberts, Molecular Biology of the Cell, Garland Science, 5th edition, 2008
  2. B. Alberts, Molecular Biology of the Cell, Garland Science, 5th edition, 2008
  3. Regulatory Proteins, (n.d.), [Online], Available: http://www.uic.edu/classes/phyb/phyb516/regulatoryproteinsu3.htm [27 November 2013]
  4. R.D Keynes, D.J Aidley, Nerve and Muscle, 3rd edition, Cambridge University Press, 2001
  5. B.Alberts, Molecular Biology of the Cell, 5th edition, Garland Science, 2008
  6. San Diego State University (unknown), Skeletal Muscle Structure and Function, http://www-rohan.sdsu.edu/course/ens304/public_html/section1/Muscle.htm
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