Journal article
Effects of Protein Kinase A Phosphorylation on Signaling between Cardiac Troponin I and the N-Terminal Domain of Cardiac Troponin C
Biochemistry (Easton), Vol.36(43), pp.13305-13311
10/28/1997
Handle:
https://hdl.handle.net/2376/103102
PMID: 9341222
Abstract
During β-adrenergic stimulation of the heart, there is a decrease in myofilament Ca2+ sensitivity mediated by the protein kinase A-(PKA-) induced phosphorylation of troponin I (cTnI). Phosphorylation, which occurs at Ser 23 and Ser 24 in an amino-terminal extension unique to cTnI, decreases the Ca2+ affinity of the amino-terminal regulatory site of cardiac troponin C (cTnC). In view of the antiparallel organization of the cTnI−cTnC complex [Krudy, G. A., Kleerekoper, Q., Guo, X., Howarth, J. W., Solaro, R. J., and Rosevear, P. R. (1994) J. Biol. Chem. 269, 23731−23735], it is not clear how the phosphorylation signal at one end of the complex affects the Ca2+ binding site at the other end. To address this question, we probed the interaction between cTnI and cTnC fragments, cTnC1 - 89 and cTnC90 - 162 (recombinant peptides corresponding to the N- and C-domains of cTnC). cTnI-Cys 5 mutant (S5C/C81I/C98S) and cTnC1 - 89 were fluorescently labeled with IAANS. When cTnI was phosphorylated, the affinity of Ca2+ for the cTnI−cTnC1-89 complex decreased significantly as indicated by a shift in the pCa50 value from 6.65 to 5.25. Upon phosphorylation, the affinity of cTnI for cTnC1 - 89 decreased by 3.8-fold in the absence of Ca2+ and 1.7-fold in the presence of Ca2+. In contrast to the case with full-length cTnC, neither cTnC1 - 89 nor cTnC90 - 162 induced significant structural changes in cTnI-Cys 5 as determined from intersite distance measurements between Cys 5 and Trp 192. Moreover, neither fragment of cTnC could significantly restore Ca2+ regulation of force generation, when exchanged into fiber bundles from which cTnC had been extracted. Our findings indicate that the transduction of PKA-induced phosphorylation signal from cTnI to the regulatory site of cTnC involves a global change in cTnI structure.
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Details
- Title
- Effects of Protein Kinase A Phosphorylation on Signaling between Cardiac Troponin I and the N-Terminal Domain of Cardiac Troponin C
- Creators
- Murali ChandraWen-Ji DongBo-Sheng PanHerbert C CheungR. John Solaro
- Publication Details
- Biochemistry (Easton), Vol.36(43), pp.13305-13311
- Academic Unit
- Integrative Physiology and Neuroscience, Department of; Chemical Engineering and Bioengineering, School of
- Publisher
- American Chemical Society
- Identifiers
- 99900546793301842
- Language
- English
- Resource Type
- Journal article