The C-Terminus of Troponin T Is Essential for Maintaining the Inactive State of Regulated Actin

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• 作者：Andrew  ; J. Franklin^&dagger ; ; Tamatha Baxley^&dagger ; ; Tomoyoshi Kobayashi^&Dagger ; ; Joseph  ; M. Chalovich^&dagger ; ; ^{chalovichj@ecu.edu}
• 刊名：Biophysical Journal
• 出版年：2012
• 出版时间：6 June, 2012
• 年：2012
• 卷：102
• 期：11
• 页码：2536-2544
• 全文大小：289 K

文摘

Striated muscle contraction is regulated by the actin binding proteins tropomyosin and troponin. Defects in these proteins lead to myopathies and cardiomyopathies. Deletion of the 14 C-terminal residues of cardiac troponin T leads to hypertrophic cardiomyopathy. We showed earlier that regulated actin containing ¦¤14 TnT was more readily activated than wild-type regulated actin. We suggested that the equilibria among the inactive (blocked), intermediate (closed or calcium), and active (open or myosin) states was shifted to the active state. We now show that, in addition, such regulated actin filaments cannot enter the inactive or blocked state. Regulated actin containing ¦¤14 TnT had ATPase activities in the absence of Ca²⁺ that were higher than wild-type filaments but far below the fully active rate. The rapid dissociation of S1-ATP from regulated actin filaments containing ¦¤14 TnT and acrylodan-labeled tropomyosin did not show the fluorescence increase characteristic of moving to the inactive state. Replacing wild-type TnI with S45E TnI, that favors the inactive state, did not restore the fluorescence change. We conclude that TnT has a previously unrecognized role in forming the inactive state of regulated actin.