Effect of Hypertrophic Cardiomyopathy Linked Troponin C Mutations and Troponin I Phosphorylation on the Rate of Calcium Dissociation from the Thin Filament

Abstract

The objective of this work was to investigate the effect of hypertrophic cardiomyopathy linked A8V, E134D and D145E mutations on the rate of calcium dissociation from cardiac troponin C (cTn)C on the thin filament under different phosphorylation states of cTnI. While the E134D mutation did not affect the rate of calcium dissociation, the A8V and D145E mutations led to significantly slower rates of calcium dissociation from cTnC on the thin filament. The effect of A8V, E134D and D145E mutations on the rate of calcium dissociation from the thin filament was also examined after cTnI was replaced by either PKA (S22D/S23DcTnI) or PKC (S41D/S43DcTnI) phosphorylation mimetic of cTnI. Replacement of cTnI by either the PKA or PKC phosphorylation mimetic of cTnI dramatically accelerated calcium dissociation from wild-type cTnC on the thin filament. The A8V mutation still led to significantly slower rate of calcium dissociation from cTnC on the thin filament after cTnI was replaced by the PKA phosphorylation mimetic of cTnI. However, in the presence of PKC phosphorylation mimetic of cTnI, the ability of A8V mutation to slow the rate of calcium dissociation from the cTnC on thin filament was abolished. The E134D mutation exerted minor to no effect on the rate of calcium dissociation from cTnC on the thin filament regardless of cTnI phosphorylation status. On the other hand, the D145E mutation led to significantly slower rates of calcium dissociation from cTnC on the thin filament after cTnI was replaced by either PKA or PKC phosphorylation mimetic of cTnI. Thus, the ability of hypertrophic cardiomyopathy linked cTnC mutations to affect the rate of calcium dissociation from cTnC on the thin filament varies depending on phosphorylation status of cTnI.