Evidence that both Ca2+-specific sites of skeletal muscle TnC are required for full activity

Zelin Sheng, William L. Strauss, Jean Marie Francois, James D. Potter

Research output: Contribution to journalArticle

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Abstract

To investigate the role of the Ca2+-specific (I and II) sites of fast skeletal muscle troponin C (TnC) in the regulation of contraction, we have produced two TnC mutants which have lost the ability to bind Ca2+ at either site I (VG1) or at site II (VG2). Both mutants were able to partially restore force to TnC-depleted skinned muscle fibers (∼25% for VG1 and ∼50% for VG2). In contrast, bovine cardiac TnC (BCTnC), which like VG1 binds Ca2+ only at site II, could fully reactivate the contraction of TnC-depleted fibers. Higher concentrations of both mutants were required to restore force to the TnC-depleted fibers than with wild type TnC (WTnC) or BCTnC. VG1 and VG2 substituted fibers could not bind additional WTnC, indicating that all of the TnC-binding sites were saturated with the mutant TnC's. The Ca2+ concentration required for force activation was much higher for VG1 and VG2 substituted fibers than for WTnC or BCTnC substituted fibers. Also, the steepness of force activation was much less in VG1 and VG2 versus WTnC and BCTnC substituted fibers. These results suggest cooperative interactions between sites I and II in WTnC. In contrast, BCTnC has essentially the same apparent Ca2+ affinity and steepness of force activation as does WTnC. Thus, cardiac TnC must have structural differences from WTnC which compensate for the lack of site I, while in WTnC, both Ca2+-specific sites are probably crucial for full functional activity.

Original languageEnglish
Pages (from-to)21554-21560
Number of pages7
JournalJournal of Biological Chemistry
Volume265
Issue number35
StatePublished - Dec 15 1990
Externally publishedYes

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Troponin C
Muscle
Skeletal Muscle
Fibers
Chemical activation
Binding Sites
Muscles

ASJC Scopus subject areas

  • Biochemistry

Cite this

Sheng, Z., Strauss, W. L., Francois, J. M., & Potter, J. D. (1990). Evidence that both Ca2+-specific sites of skeletal muscle TnC are required for full activity. Journal of Biological Chemistry, 265(35), 21554-21560.

Evidence that both Ca2+-specific sites of skeletal muscle TnC are required for full activity. / Sheng, Zelin; Strauss, William L.; Francois, Jean Marie; Potter, James D.

In: Journal of Biological Chemistry, Vol. 265, No. 35, 15.12.1990, p. 21554-21560.

Research output: Contribution to journalArticle

Sheng, Z, Strauss, WL, Francois, JM & Potter, JD 1990, 'Evidence that both Ca2+-specific sites of skeletal muscle TnC are required for full activity', Journal of Biological Chemistry, vol. 265, no. 35, pp. 21554-21560.
Sheng, Zelin ; Strauss, William L. ; Francois, Jean Marie ; Potter, James D. / Evidence that both Ca2+-specific sites of skeletal muscle TnC are required for full activity. In: Journal of Biological Chemistry. 1990 ; Vol. 265, No. 35. pp. 21554-21560.
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