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N-terminal extension in cardiac myosin-binding protein C regulates myofilament binding.

ABSTRACT: RATIONALE:Mutations in the gene encoding the sarcomeric protein cardiac myosin-binding protein C (cMyBP-C) are a leading cause of hypertrophic cardiomyopathy (HCM). Mouse models targeting cMyBP-C and use of recombinant proteins have been effective in studying its roles in contractile function and disease. Surprisingly, while the N-terminus of cMyBP-C is important to regulate myofilament binding and contains many HCM mutations, an incorrect sequence, lacking the N-terminal 8 amino acids has been used in many studies. OBJECTIVES:To determine the N-terminal cMyBP-C sequences in ventricles and investigate the roles of species-specific differences in cMyBP-C on myofilament binding. METHODS AND RESULTS:We determined cMyBP-C sequences in mouse and human by inspecting available sequence databases. N-terminal differences were confirmed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cosedimentation assays with actin or myosin were used to examine binding in mouse, human and chimeric fusion proteins of cMyBP-C. Time-resolved FRET (TR-FRET) with site-directed probes on cMyBP-C was employed to measure structural dynamics. LC-MS/MS supported the sequencing data that mouse cMyBP-C contains an eight-residue N-terminal extension (NTE) not found in human. Cosedimentation assays revealed that cardiac myosin binding was strongly influenced by the presence of the NTE, which reduced binding by 60%. 75% more human C0-C2 than mouse bound to myosin. Actin binding of mouse C0-C2 was not affected by the NTE. 50% more human C0-C2 than mouse bound to actin. TR-FRET indicates that the NTE did not significantly affect structural dynamics across domains C0 and C1. CONCLUSIONS:Our functional results are consistent with the idea that cardiac myosin binding of N-terminal cMyBP-C is reduced in the mouse protein due to the presence of the NTE, which is proposed to interfere with myosin regulatory light chain (RLC) binding. The NTE is a critical component of mouse cMyBP-C, and should be considered in extrapolation of studies to cMyBP-C and HCM mechanisms in human.

SUBMITTER: Bunch TA

PROVIDER: S-EPMC6366860 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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N-terminal extension in cardiac myosin-binding protein C regulates myofilament binding.

Bunch Thomas A TA Lepak Victoria C VC Kanassatega Rhye-Samuel RS Colson Brett A BA

Journal of molecular and cellular cardiology 20181022

<h4>Rationale</h4>Mutations in the gene encoding the sarcomeric protein cardiac myosin-binding protein C (cMyBP-C) are a leading cause of hypertrophic cardiomyopathy (HCM). Mouse models targeting cMyBP-C and use of recombinant proteins have been effective in studying its roles in contractile function and disease. Surprisingly, while the N-terminus of cMyBP-C is important to regulate myofilament binding and contains many HCM mutations, an incorrect sequence, lacking the N-terminal 8 amino acids h ...[more]

PMID: 30359561

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Project description:Cardiac myosin binding protein-C (cMyBP-C) plays a role in sarcomeric structure and stability, as well as modulating heart muscle contraction. The 150 kDa full-length (FL) cMyBP-C has been shown to undergo proteolytic cleavage during ischemia-reperfusion injury, producing an N-terminal 40 kDa fragment (mass 29 kDa) that is predominantly associated with post-ischemic contractile dysfunction. Thus far, the pathogenic properties of such truncated cMyBP-C proteins have not been elucidated. In the present study, we hypothesized that the presence of these 40 kDa fragments is toxic to cardiomyocytes, compared to the 110 kDa C-terminal fragment and FL cMyBP-C. To test this hypothesis, we infected neonatal rat ventricular cardiomyocytes and adult rabbit ventricular cardiomyocytes with adenoviruses expressing the FL, 110 and 40 kDa fragments of cMyBP-C, and measured cytotoxicity, Ca(2+) transients, contractility, and protein-protein interactions. Here we show that expression of 40 kDa fragments in neonatal rat ventricular cardiomyocytes significantly increases LDH release and caspase 3 activity, significantly reduces cell viability, and impairs Ca(2+) handling. Adult cardiomyocytes expressing 40 kDa fragments exhibited similar impairment of Ca(2+) handling along with a significant reduction of sarcomere length shortening, relaxation velocity, and contraction velocity. Pull-down assays using recombinant proteins showed that the 40 kDa fragment binds significantly to sarcomeric actin, comparable to C0-C2 domains. In addition, we discovered several acetylation sites within the 40 kDa fragment that could potentially affect actomyosin function. Altogether, our data demonstrate that the 40 kDa cleavage fragments of cMyBP-C are toxic to cardiomyocytes and significantly impair contractility and Ca(2+) handling via inhibition of actomyosin function. By elucidating the deleterious effects of endogenously expressed cMyBP-C N-terminal fragments on sarcomere function, these data contribute to the understanding of contractile dysfunction following myocardial injury.

Dataset Information

N-terminal extension in cardiac myosin-binding protein C regulates myofilament binding.

Publications

N-terminal extension in cardiac myosin-binding protein C regulates myofilament binding.

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