Divergent effects of α- and β-myosin heavy chain isoforms on the N terminus of rat cardiac troponin T

Ranganath Mamidi; Murali Chandra

doi:10.1085/jgp.201310971

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Divergent effects of α- and β-myosin heavy chain isoforms on the N terminus of rat cardiac troponin T

Journal article

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Divergent effects of α- and β-myosin heavy chain isoforms on the N terminus of rat cardiac troponin T

Ranganath Mamidi and Murali Chandra

The Journal of general physiology, Vol.142(4), pp.413-423

10/2013

DOI: https://doi.org/10.1085/jgp.201310971

Handle:

https://hdl.handle.net/2376/107789

PMCID: PMC3787779

PMID: 24043862

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Abstract

Protein Structure, Tertiary

Troponin T - genetics

Amino Acid Sequence

Calcium - metabolism

Sarcomeres - drug effects

Sarcomeres - metabolism

Molecular Sequence Data

Rats

Male

Troponin T - chemistry

Myosin Heavy Chains - metabolism

Rats, Sprague-Dawley

Propylthiouracil - pharmacology

Troponin T - metabolism

Animals

Muscle Contraction

Protein Isoforms - metabolism

Ventricular Myosins - metabolism

Mutation

Sarcomeres - physiology

Divergent effects of α- and β-myosin heavy chain (MHC) isoforms on contractile behavior arise mainly because of their impact on thin filament cooperativity. The N terminus of cardiac troponin T (cTnT) also modulates thin filament cooperativity. Our hypothesis is that the impact of the N terminus of cTnT on thin filament activation is modulated by a shift from α- to β-MHC isoform. We engineered two recombinant proteins by deleting residues 1-43 and 44-73 in rat cTnT (RcTnT): RcTnT(1-43Δ) and RcTnT(44-73Δ), respectively. Dynamic and steady-state contractile parameters were measured at sarcomere length of 2.3 µm after reconstituting proteins into detergent-skinned muscle fibers from normal (α-MHC) and propylthiouracil-treated (β-MHC) rat hearts. α-MHC attenuated Ca(2+)-activated maximal tension (∼46%) in RcTnT(1-43Δ) fibers. In contrast, β-MHC decreased tension only by 19% in RcTnT(1-43Δ) fibers. Both α- and β-MHC did not affect tension in RcTnT(44-73Δ) fibers. The instantaneous muscle fiber stiffness measurements corroborated the divergent impact of α- and β-MHC on tension in RcTnT(1-43Δ) fibers. pCa50 (-log of [Ca(2+)]free required for half-maximal activation) decreased significantly by 0.13 pCa units in α-MHC + RcTnT(1-43Δ) fibers but remained unaltered in β-MHC + RcTnT(1-43Δ) fibers, demonstrating that β-MHC counteracted the attenuating effect of RcTnT(1-43Δ) on myofilament Ca(2+) sensitivity. β-MHC did not alter the sudden stretch-mediated recruitment of new cross-bridges (ER) in RcTnT(1-43Δ) fibers, but α-MHC attenuated ER by 36% in RcTnT(1-43Δ) fibers. The divergent impact of α- and β-MHC on how the N terminus of cTnT modulates contractile dynamics has implications for heart disease; alterations in cTnT and MHC are known to occur via changes in isoform expression or mutations.

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Title: Divergent effects of α- and β-myosin heavy chain isoforms on the N terminus of rat cardiac troponin T
Creators: Ranganath Mamidi - Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164
Murali Chandra
Publication Details: The Journal of general physiology, Vol.142(4), pp.413-423
Academic Unit: Integrative Physiology and Neuroscience, Department of
Publisher: United States
Grant note: R01 HL075643 / NHLBI NIH HHS R01-HL-075643 / NHLBI NIH HHS
Identifiers: 99900547204701842
Language: English
Resource Type: Journal article