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Reverse actin sliding triggers strong myosin binding that moves tropomyosin.

Publication ,  Journal Article
Bekyarova, TI; Reedy, MC; Baumann, BAJ; Tregear, RT; Ward, A; Krzic, U; Prince, KM; Perz-Edwards, RJ; Reconditi, M; Gore, D; Irving, TC; Reedy, MK
Published in: Proc Natl Acad Sci U S A
July 29, 2008

Actin/myosin interactions in vertebrate striated muscles are believed to be regulated by the "steric blocking" mechanism whereby the binding of calcium to the troponin complex allows tropomyosin (TM) to change position on actin, acting as a molecular switch that blocks or allows myosin heads to interact with actin. Movement of TM during activation is initiated by interaction of Ca(2+) with troponin, then completed by further displacement by strong binding cross-bridges. We report x-ray evidence that TM in insect flight muscle (IFM) moves in a manner consistent with the steric blocking mechanism. We find that both isometric contraction, at high [Ca(2+)], and stretch activation, at lower [Ca(2+)], develop similarly high x-ray intensities on the IFM fourth actin layer line because of TM movement, coinciding with x-ray signals of strong-binding cross-bridge attachment to helically favored "actin target zones." Vanadate (Vi), a phosphate analog that inhibits active cross-bridge cycling, abolishes all active force in IFM, allowing high [Ca(2+)] to elicit initial TM movement without cross-bridge attachment or other changes from relaxed structure. However, when stretched in high [Ca(2+)], Vi-"paralyzed" fibers produce force substantially above passive response at pCa approximately 9, concurrent with full conversion from resting to active x-ray pattern, including x-ray signals of cross-bridge strong-binding and TM movement. This argues that myosin heads can be recruited as strong-binding "brakes" by backward-sliding, calcium-activated thin filaments, and are as effective in moving TM as actively force-producing cross-bridges. Such recruitment of myosin as brakes may be the major mechanism resisting extension during lengthening contractions.

Duke Scholars

Published In

Proc Natl Acad Sci U S A

DOI

EISSN

1091-6490

Publication Date

July 29, 2008

Volume

105

Issue

30

Start / End Page

10372 / 10377

Location

United States

Related Subject Headings

  • Vanadates
  • Tropomyosin
  • Stress, Mechanical
  • Protein Binding
  • Myosins
  • Muscles
  • Muscle Proteins
  • Muscle Contraction
  • Models, Biological
  • Insecta
 

Citation

APA
Chicago
ICMJE
MLA
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Bekyarova, T. I., Reedy, M. C., Baumann, B. A. J., Tregear, R. T., Ward, A., Krzic, U., … Reedy, M. K. (2008). Reverse actin sliding triggers strong myosin binding that moves tropomyosin. Proc Natl Acad Sci U S A, 105(30), 10372–10377. https://doi.org/10.1073/pnas.0709877105
Bekyarova, T. I., M. C. Reedy, B. A. J. Baumann, R. T. Tregear, A. Ward, U. Krzic, K. M. Prince, et al. “Reverse actin sliding triggers strong myosin binding that moves tropomyosin.Proc Natl Acad Sci U S A 105, no. 30 (July 29, 2008): 10372–77. https://doi.org/10.1073/pnas.0709877105.
Bekyarova TI, Reedy MC, Baumann BAJ, Tregear RT, Ward A, Krzic U, et al. Reverse actin sliding triggers strong myosin binding that moves tropomyosin. Proc Natl Acad Sci U S A. 2008 Jul 29;105(30):10372–7.
Bekyarova, T. I., et al. “Reverse actin sliding triggers strong myosin binding that moves tropomyosin.Proc Natl Acad Sci U S A, vol. 105, no. 30, July 2008, pp. 10372–77. Pubmed, doi:10.1073/pnas.0709877105.
Bekyarova TI, Reedy MC, Baumann BAJ, Tregear RT, Ward A, Krzic U, Prince KM, Perz-Edwards RJ, Reconditi M, Gore D, Irving TC, Reedy MK. Reverse actin sliding triggers strong myosin binding that moves tropomyosin. Proc Natl Acad Sci U S A. 2008 Jul 29;105(30):10372–10377.
Journal cover image

Published In

Proc Natl Acad Sci U S A

DOI

EISSN

1091-6490

Publication Date

July 29, 2008

Volume

105

Issue

30

Start / End Page

10372 / 10377

Location

United States

Related Subject Headings

  • Vanadates
  • Tropomyosin
  • Stress, Mechanical
  • Protein Binding
  • Myosins
  • Muscles
  • Muscle Proteins
  • Muscle Contraction
  • Models, Biological
  • Insecta