Elucidation of Isoform-dependent pH Sensitivity of Troponin I by NMR Spectroscopy

Robertson, Ian M.; Holmes, Peter C.; Li, Monica X.; Pineda-Sanabria, Sandra E.; Baryshnikova, Olga K.; Sykes, Brian D.

doi:10.1074/jbc.m111.301499

Cited by 13 publications

(15 citation statements)

References 57 publications

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“…Thus, improvements of the method should include more explicit considerations of metabolite concentrations, along with the effects of allostery and cooperativity, which require structural biology considerations 44 . Fourth, our knowledge-driven, homology-based pipeline might be improved by distinguishing enzyme isoforms having very different pH-activity profiles 45 , and further refined by predicting critical points of half and none activity, where less experimental data are available (Supplementary Figure 1 ).…”

Section: Discussionmentioning

confidence: 99%

Systems analysis of intracellular pH vulnerabilities for cancer therapy

et al. 2018

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A reverse pH gradient is a hallmark of cancer metabolism, manifested by extracellular acidosis and intracellular alkalization. While consequences of extracellular acidosis are known, the roles of intracellular alkalization are incompletely understood. By reconstructing and integrating enzymatic pH-dependent activity profiles into cell-specific genome-scale metabolic models, we develop a computational methodology that explores how intracellular pH (pHi) can modulate metabolism. We show that in silico, alkaline pHi maximizes cancer cell proliferation coupled to increased glycolysis and adaptation to hypoxia (i.e., the Warburg effect), whereas acidic pHi disables these adaptations and compromises tumor cell growth. We then systematically identify metabolic targets (GAPDH and GPI) with predicted amplified anti-cancer effects at acidic pHi, forming a novel therapeutic strategy. Experimental testing of this strategy in breast cancer cells reveals that it is particularly effective against aggressive phenotypes. Hence, this study suggests essential roles of pHi in cancer metabolism and provides a conceptual and computational framework for exploring pHi roles in other biomedical domains.

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Section: Discussionmentioning

confidence: 99%

Systems analysis of intracellular pH vulnerabilities for cancer therapy

et al. 2018

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“…Simulations with A164H cTnI showed the potential for a similar electrostatic interaction between H164 and E19 of cTnC (Palpant et al, ). Nuclear magnetic resonance (NMR) studies using similar portions of sTnI and A164H bound to cTnC in acidic conditions support the potential for a histidine to E19 interaction (Pineda‐Sanabria et al, 2012; Robertson et al, ). The NMR studies also indicate that there is increased affinity of sTnI and A164H for cTnC under acidic conditions.…”

Section: Therapeutic Use Of Stoichiometric Replacementmentioning

confidence: 95%

Cell Biology of Sarcomeric Protein Engineering: Disease Modeling and Therapeutic Potential

Thompson

Metzger²

2014

The Anatomical Record

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The cardiac sarcomere is the functional unit for myocyte contraction. Ordered arrays of sarcomeric proteins held in stoichiometric balance with each other, respond to calcium to coordinate contraction and relaxation of the heart. Altered sarcomeric structure-function underlies the primary basis of disease in multiple acquired and inherited heart disease states. Hypertrophic and restrictive cardiomyopathies are caused by inherited mutations in sarcomeric genes and result in altered contractility. Ischemia mediated acidosis directly alters sarcomere function resulting in decreased contractility. In this review, we highlight the use of acute genetic engineering of adult cardiac myocytes through stoichiometric replacement of sarcomeric proteins in these disease states with particular focus on cardiac troponin I. Stoichiometric replacement of disease causing mutations has been instrumental in defining the molecular mechanisms of hypertrophic and restrictive cardiomyopathy in a cellular context. In addition, taking advantage of stoichiometric replacement through gene therapy is discussed, highlighting the ischemia-resistant histidine-button, A164H cTnI. Stoichiometric replacement of sarcomeric proteins offers a potential gene therapy avenue to replace mutant proteins, alter sarcomeric responses to pathophysiologic insults or neutralize altered sarcomeric function in disease.

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“…The positively charged imidazole ring of His130 forms a salt bridge with Glu19 on the surface of cNTnC, stabilizing the cNTnC-ssTnI complex and restoring Ca 2+ -binding affinity under acidic conditions 43 . In the complex, His130 has a pKa of ~6.7 44 , becoming more positively charged as the intracellular pH drops below 7. Recent NMR studies of cNTnC•Ca 2+ bound to fsTnI 115 -131, as well as cNTnC•Ca 2+ bound to A162H–cTnI1 47 -163, have confirmed the importance of this electrostatic interaction 45 .…”

Section: Structure and Function Of Cardiac Troponin C Within The Tropmentioning

confidence: 99%

Structure and function of cardiac troponin C (TNNC1): Implications for heart failure, cardiomyopathies, and troponin modulating drugs

Hwang

2015

Gene

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113

105

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In striated muscle, the protein troponin complex turns contraction on and off in a calcium-dependent manner. The calcium-sensing component of the complex is troponin C, which is expressed from the TNNC1 gene in both cardiac muscle and slow-twitch skeletal muscle (identical transcript in both tissues) and the TNNC2 gene in fast-twitch skeletal muscle. Cardiac troponin C (cTnC) is made up of two globular EF-hand domains connected by a flexible linker. The structural C-domain (cCTnC) contains two high affinity calcium-binding sites that are always occupied by Ca2+ or Mg2+ under physiologic conditions, stabilizing an open conformation that remains anchored to the rest of the troponin complex. In contrast, the regulatory N-domain (cNTnC) contains a single low affinity site that is largely unoccupied at resting calcium concentrations. During muscle activation, calcium binding to cNTnC favors an open conformation that binds to the switch region of troponin I, removing adjacent inhibitory regions of troponin I from actin and allowing muscle contraction to proceed. Regulation of the calcium binding affinity of cNTnC is physiologically important, because it directly impacts the calcium sensitivity of muscle contraction. Calcium sensitivity can be modified by drugs that stabilize the open form of cNTnC, post-translational modifications like phosphorylation of troponin I, or downstream thin filament protein interactions that impact the availability of the troponin I switch region. Recently, mutations in cTnC have been associated with hypertrophic or dilated cardiomyopathy. A detailed understanding of how calcium sensitivity is regulated through the troponin complex is necessary for explaining how mutations perturb its function to promote cardiomyopathy and how post-translational modifications in the thin filament affect heart function and heart failure. Troponin modulating drugs are being developed for the treatment of cardiomyopathies and heart failure.

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Elucidation of Isoform-dependent pH Sensitivity of Troponin I by NMR Spectroscopy

Cited by 13 publications

References 57 publications

Systems analysis of intracellular pH vulnerabilities for cancer therapy

Systems analysis of intracellular pH vulnerabilities for cancer therapy

Cell Biology of Sarcomeric Protein Engineering: Disease Modeling and Therapeutic Potential

Structure and function of cardiac troponin C (TNNC1): Implications for heart failure, cardiomyopathies, and troponin modulating drugs

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