Tropomyosin: Difference between revisions

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<blockquote>&nbsp;First discovered by Bailey (Bailey, 1948), the tropomyosins are a group of proteins that bind to the sides of actin filaments and (together with troponins) regulate the interaction of the filaments with myosin in response to Ca2+. They are parallel, a-helical, coiled coil dimers. Vertebrates typically express in the region of 20 different tropomyosins from alternative spicing from about four tropomyosin genes (Perry, 2001 ). Tropomyosins exist as both homo-dimers and hetero-dimers held together by a series of salt bridges and hydrophobic interactions. They may also interact through their N and C termini in solution (especially in low ionic strength buffers) and this can be monitored by viscosity. There are two major groups of tropomyosin the high and low molecular weight tropomyosins. The former type exist primarily in muscle tissues (cardiac, smooth and skeletal) whereas non-muscle tissues express both high and low mol.wt. tropomyosins.<ref>University of Edinburgh, 'Tropomyosin', http://www.bms.ed.ac.uk/research/others/smaciver/encyclop/Abp-t/Tropomyosin.htm, 2003</ref></blockquote>
According to B. Alberts<ref>B. Alberts, Molecular Biology of the Cell, Garland Science, 5th edition, 2008</ref> tropomyosin is an elongated [[Protein|protein]], which stabilizes [[Actin filaments|actin filaments]] by binding to seven adjacent [[Actin|actin]] subunits, thus preventing it from interacting with other proteins&nbsp;<ref>B. Alberts, Molecular Biology of the Cell, Garland Science, 5th edition, 2008</ref>. Tropomyosin has a coiled coil structure caused by the joining of two alpha helical monomers&nbsp;<ref>Regulatory Proteins, (n.d.), [Online], Available: http://www.uic.edu/classes/phyb/phyb516/regulatoryproteinsu3.htm [27 November 2013]</ref>.&nbsp;Tropomyosin, along with [[Troponin|troponin]] play an important role in regulation of [[Muscle|muscle]] contraction&nbsp;<ref>R.D Keynes, D.J Aidley, Nerve and Muscle, 3rd edition, Cambridge University Press, 2001</ref>.&nbsp;As tropomyosin binds to actin it follows its helical structure&nbsp;<ref>B.Alberts, Molecular Biology of the Cell, 5th edition, Garland Science, 2008</ref>. Fig.1
<references /><br>
 
[[Image:Tropomyosin.gif|Accessory proteins troponin and tropomyosin on the actin filament]]<ref>San Diego State University (unknown), Skeletal Muscle Structure and Function, http://www-rohan.sdsu.edu/course/ens304/public_html/section1/Muscle.htm</ref>  
 
This figure describes the relative position of accesory proteins and [[Actin filaments|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  ===
 
<references />

Latest revision as of 05:15, 29 November 2013

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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