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Disease-related cardiac troponins alter thin filament Ca2+ association and dissociation rates.

Liu B, Tikunova SB, Kline KP, Siddiqui JK, Davis JP - PLoS ONE (2012)

Bottom Line: By utilizing an IAANS labeled fluorescent troponin C, [Formula: see text], we examined the effects of ten disease-related troponin modifications on the Ca(2+) binding properties of the troponin complex and the reconstituted thin filament.Consistent with previous studies, the majority of the protein modifications had no effect on the Ca(2+) binding properties of the isolated troponin complex.The protein modifications also increased (up to 5.4-fold) or decreased (up to 2.5-fold) the apparent rate of Ca(2+) association to the thin filament.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, United States of America.

ABSTRACT
The contractile response of the heart can be altered by disease-related protein modifications to numerous contractile proteins. By utilizing an IAANS labeled fluorescent troponin C, [Formula: see text], we examined the effects of ten disease-related troponin modifications on the Ca(2+) binding properties of the troponin complex and the reconstituted thin filament. The selected modifications are associated with a broad range of cardiac diseases: three subtypes of familial cardiomyopathies (dilated, hypertrophic and restrictive) and ischemia-reperfusion injury. Consistent with previous studies, the majority of the protein modifications had no effect on the Ca(2+) binding properties of the isolated troponin complex. However, when incorporated into the thin filament, dilated cardiomyopathy mutations desensitized (up to 3.3-fold), while hypertrophic and restrictive cardiomyopathy mutations, and ischemia-induced truncation of troponin I, sensitized the thin filament to Ca(2+) (up to 6.3-fold). Kinetically, the dilated cardiomyopathy mutations increased the rate of Ca(2+) dissociation from the thin filament (up to 2.5-fold), while the hypertrophic and restrictive cardiomyopathy mutations, and the ischemia-induced truncation of troponin I decreased the rate (up to 2-fold). The protein modifications also increased (up to 5.4-fold) or decreased (up to 2.5-fold) the apparent rate of Ca(2+) association to the thin filament. Thus, the disease-related protein modifications alter Ca(2+) binding by influencing both the association and dissociation rates of thin filament Ca(2+) exchange. These alterations in Ca(2+) exchange kinetics influenced the response of the thin filament to artificial Ca(2+) transients generated in a stopped-flow apparatus. Troponin C may act as a hub, sensing physiological and pathological stimuli to modulate the Ca(2+)-binding properties of the thin filament and influence the contractile performance of the heart.

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Effect of disease-related protein modifications on the rate of Ca2+ association to the thin filament.Panel A shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound control  at 5 µM, 10 µM and 20 µM Ca2+ ([Ca2+] after mixing). Panel B shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound TnI(1-192)  at 2.5 µM, 5 µM and 10 µM Ca2+. The rate of the fluorescence increase when Ca2+ associates with the thin filament was fit with a single exponential to calculate the observed rate (kobserved). All  complexes consist of the full length Tn subunits of , TnI and TnT, except for ischemic related truncated TnI (1-192). The disease related modification is either in TnI or TnT, in either case, the other protein (TnT or TnI) was wild type. Panel C shows the plots of kobserved versus [Ca2+] for thin filament bound control  (□) and TnI (1-192)  (). The rate of Ca2+ association to the thin filament was obtained by calculating the slope of a linear fit to the data. Panel D shows the plots of kobserved versus [Ca2+] for thin filament bound TnI R192H  (▵), TnI D190H  (▽), TnT ΔK210  (⋆), and TnT R131W  (○).
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pone-0038259-g006: Effect of disease-related protein modifications on the rate of Ca2+ association to the thin filament.Panel A shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound control at 5 µM, 10 µM and 20 µM Ca2+ ([Ca2+] after mixing). Panel B shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound TnI(1-192) at 2.5 µM, 5 µM and 10 µM Ca2+. The rate of the fluorescence increase when Ca2+ associates with the thin filament was fit with a single exponential to calculate the observed rate (kobserved). All complexes consist of the full length Tn subunits of , TnI and TnT, except for ischemic related truncated TnI (1-192). The disease related modification is either in TnI or TnT, in either case, the other protein (TnT or TnI) was wild type. Panel C shows the plots of kobserved versus [Ca2+] for thin filament bound control (□) and TnI (1-192) (). The rate of Ca2+ association to the thin filament was obtained by calculating the slope of a linear fit to the data. Panel D shows the plots of kobserved versus [Ca2+] for thin filament bound TnI R192H (▵), TnI D190H (▽), TnT ΔK210 (⋆), and TnT R131W (○).

Mentions: The kinetic studies indicate that the changes in Ca2+ sensitivity of the thin filament caused by the protein modifications are in part due to changes in the rate of Ca2+ dissociation. However, as shown in table 2 and figure 5, there was only a weak correlation (r2 = 0.17, fit not shown) between the changes in the thin filament Ca2+ sensitivities and the changes in the Ca2+ dissociation rates for the different protein modifications. These results suggest that the rate of Ca2+ association to the thin filament can also be altered by the protein modifications. To test this hypothesis, stopped-flow experiments were performed to measure the rate of Ca2+ association to the thin filaments containing TnI R192H, D190H, TnI (1-192), TnT ΔK210 and TnT R131W. Based on the calculated rate of Ca2+ association, TnT R131W was predicted to have little effect on the rate of Ca2+ association while the rest of the protein modifications were expected to significantly change the rate of Ca2+ association (Table 2). Using a traditional approach to determine the apparent Ca2+ association rate to the thin filament, the measured rate of Ca2+ association to the control thin filament was 9±1×106 M−1s−1 (Figure 6A, 6C and Table 2). Consistent with the calculated Ca2+ association rates, TnI R192H, D190H and TnI (1-192) increased the apparent rate of Ca2+ association to the thin filament by ∼ 4- to 5-fold (Figure 6B, 6D and Table 2). In contrast, TnT ΔK210 slowed the apparent rate of Ca2+ association to the thin filament by ∼3-fold (Figure 6D and Table 2). On the other hand, the apparent rate of Ca2+ association to the thin filament containing TnT R131W was similar to that of the control thin filament, with the rate being 12±1×106 M−1s−1 (Figure 6D and Table 2). Thus, the experimental results indicate that the apparent rate of Ca2+ association to the thin filament can also be altered by the disease-related protein modifications.


Disease-related cardiac troponins alter thin filament Ca2+ association and dissociation rates.

Liu B, Tikunova SB, Kline KP, Siddiqui JK, Davis JP - PLoS ONE (2012)

Effect of disease-related protein modifications on the rate of Ca2+ association to the thin filament.Panel A shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound control  at 5 µM, 10 µM and 20 µM Ca2+ ([Ca2+] after mixing). Panel B shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound TnI(1-192)  at 2.5 µM, 5 µM and 10 µM Ca2+. The rate of the fluorescence increase when Ca2+ associates with the thin filament was fit with a single exponential to calculate the observed rate (kobserved). All  complexes consist of the full length Tn subunits of , TnI and TnT, except for ischemic related truncated TnI (1-192). The disease related modification is either in TnI or TnT, in either case, the other protein (TnT or TnI) was wild type. Panel C shows the plots of kobserved versus [Ca2+] for thin filament bound control  (□) and TnI (1-192)  (). The rate of Ca2+ association to the thin filament was obtained by calculating the slope of a linear fit to the data. Panel D shows the plots of kobserved versus [Ca2+] for thin filament bound TnI R192H  (▵), TnI D190H  (▽), TnT ΔK210  (⋆), and TnT R131W  (○).
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3366952&req=5

pone-0038259-g006: Effect of disease-related protein modifications on the rate of Ca2+ association to the thin filament.Panel A shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound control at 5 µM, 10 µM and 20 µM Ca2+ ([Ca2+] after mixing). Panel B shows the kinetic traces (an average of 3 to 5 individual traces collected at least 9 times) observed for Ca2+ association to thin filament bound TnI(1-192) at 2.5 µM, 5 µM and 10 µM Ca2+. The rate of the fluorescence increase when Ca2+ associates with the thin filament was fit with a single exponential to calculate the observed rate (kobserved). All complexes consist of the full length Tn subunits of , TnI and TnT, except for ischemic related truncated TnI (1-192). The disease related modification is either in TnI or TnT, in either case, the other protein (TnT or TnI) was wild type. Panel C shows the plots of kobserved versus [Ca2+] for thin filament bound control (□) and TnI (1-192) (). The rate of Ca2+ association to the thin filament was obtained by calculating the slope of a linear fit to the data. Panel D shows the plots of kobserved versus [Ca2+] for thin filament bound TnI R192H (▵), TnI D190H (▽), TnT ΔK210 (⋆), and TnT R131W (○).
Mentions: The kinetic studies indicate that the changes in Ca2+ sensitivity of the thin filament caused by the protein modifications are in part due to changes in the rate of Ca2+ dissociation. However, as shown in table 2 and figure 5, there was only a weak correlation (r2 = 0.17, fit not shown) between the changes in the thin filament Ca2+ sensitivities and the changes in the Ca2+ dissociation rates for the different protein modifications. These results suggest that the rate of Ca2+ association to the thin filament can also be altered by the protein modifications. To test this hypothesis, stopped-flow experiments were performed to measure the rate of Ca2+ association to the thin filaments containing TnI R192H, D190H, TnI (1-192), TnT ΔK210 and TnT R131W. Based on the calculated rate of Ca2+ association, TnT R131W was predicted to have little effect on the rate of Ca2+ association while the rest of the protein modifications were expected to significantly change the rate of Ca2+ association (Table 2). Using a traditional approach to determine the apparent Ca2+ association rate to the thin filament, the measured rate of Ca2+ association to the control thin filament was 9±1×106 M−1s−1 (Figure 6A, 6C and Table 2). Consistent with the calculated Ca2+ association rates, TnI R192H, D190H and TnI (1-192) increased the apparent rate of Ca2+ association to the thin filament by ∼ 4- to 5-fold (Figure 6B, 6D and Table 2). In contrast, TnT ΔK210 slowed the apparent rate of Ca2+ association to the thin filament by ∼3-fold (Figure 6D and Table 2). On the other hand, the apparent rate of Ca2+ association to the thin filament containing TnT R131W was similar to that of the control thin filament, with the rate being 12±1×106 M−1s−1 (Figure 6D and Table 2). Thus, the experimental results indicate that the apparent rate of Ca2+ association to the thin filament can also be altered by the disease-related protein modifications.

Bottom Line: By utilizing an IAANS labeled fluorescent troponin C, [Formula: see text], we examined the effects of ten disease-related troponin modifications on the Ca(2+) binding properties of the troponin complex and the reconstituted thin filament.Consistent with previous studies, the majority of the protein modifications had no effect on the Ca(2+) binding properties of the isolated troponin complex.The protein modifications also increased (up to 5.4-fold) or decreased (up to 2.5-fold) the apparent rate of Ca(2+) association to the thin filament.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio, United States of America.

ABSTRACT
The contractile response of the heart can be altered by disease-related protein modifications to numerous contractile proteins. By utilizing an IAANS labeled fluorescent troponin C, [Formula: see text], we examined the effects of ten disease-related troponin modifications on the Ca(2+) binding properties of the troponin complex and the reconstituted thin filament. The selected modifications are associated with a broad range of cardiac diseases: three subtypes of familial cardiomyopathies (dilated, hypertrophic and restrictive) and ischemia-reperfusion injury. Consistent with previous studies, the majority of the protein modifications had no effect on the Ca(2+) binding properties of the isolated troponin complex. However, when incorporated into the thin filament, dilated cardiomyopathy mutations desensitized (up to 3.3-fold), while hypertrophic and restrictive cardiomyopathy mutations, and ischemia-induced truncation of troponin I, sensitized the thin filament to Ca(2+) (up to 6.3-fold). Kinetically, the dilated cardiomyopathy mutations increased the rate of Ca(2+) dissociation from the thin filament (up to 2.5-fold), while the hypertrophic and restrictive cardiomyopathy mutations, and the ischemia-induced truncation of troponin I decreased the rate (up to 2-fold). The protein modifications also increased (up to 5.4-fold) or decreased (up to 2.5-fold) the apparent rate of Ca(2+) association to the thin filament. Thus, the disease-related protein modifications alter Ca(2+) binding by influencing both the association and dissociation rates of thin filament Ca(2+) exchange. These alterations in Ca(2+) exchange kinetics influenced the response of the thin filament to artificial Ca(2+) transients generated in a stopped-flow apparatus. Troponin C may act as a hub, sensing physiological and pathological stimuli to modulate the Ca(2+)-binding properties of the thin filament and influence the contractile performance of the heart.

Show MeSH
Related in: MedlinePlus