Effects of Protein Kinase C Dependent Phosphorylation and a Familial Hypertrophic Cardiomyopathy-Related Mutation of Cardiac Troponin I on Structural Transition of Troponin C and Myofilament Activatio

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• 作者：Tomoyoshi Kobayashi ; Wen-Ji Dong ; Eileen M. Burkart ; Herbert C. Cheung ; and R. John Solaro
• 刊名：Biochemistry
• 出版年：2004
• 出版时间：May 25, 2004
• 年：2004
• 卷：43
• 期：20
• 页码：5996 - 6004
• 全文大小：141K
• 年卷期：v.43,no.20(May 25, 2004)
• ISSN：1520-4995

文摘

In experiments reported here, we compared tension and thin filament Ca²⁺ signaling inpreparations containing either wild-type cardiac troponin I (cTnI) or a mutant cTnI with an R146G mutation[cTnI(146G)] linked to familial hypertrophic cardiomyopathy. Myofilament function is altered in associationwith cTnI phosphorylation by protein kinase C (PKC), which is activated in hypertrophy. Whether thereare differential effects of PKC phosphorylation on cTnI compared to cTnI(146G) remains unknown. Wetherefore also studied cTnI and cTnI(146G) with PKC sites mutated to Glu, which mimics phosphorylation.Compared to cTnI controls, binary complexes with either cTnI(146G) or cTnI(43E/45E/144E) had a smalleffect on Ca²⁺-dependent structural opening of the N-terminal regulatory domain of cTnC as measuredusing Förster resonance energy transfer. However, this structural change was significantly reduced in thecTnC-cTnI(43E/45E/144E/146G) complex. Exchange of cTnI in skinned fiber bundles with cTnI(146G)induced enhanced Ca²⁺ sensitivity and an elevated resting tension. Exchange of cTnI with cTnI(43E/45E/144E) induced a depression in Ca²⁺ sensitivity and maximum tension. However, compared tocTnI(146G), cTnI(43E/45E/144E/146G) had little additional effects on myofilament response to Ca²⁺.By comparing activation of tension to the open state of the N-domain of cTnC with variations in the stateof cTnI, we were able to provide data supporting the hypothesis that activation of cardiac myofilamentsis tightly coupled to the open state of the N-domain of cTnC. Our data also support the hypothesis thatpathological effects of phosphorylation are influenced by mutations in cTnI.