Differential Regulation of the Actomyosin Interaction by Skeletal and Cardiac Troponin Isoforms

Maytum, Robin; Westerdorf, Barbara; Jaquet, Kornélia; Geeves, Michael A.

doi:10.1074/jbc.m210690200

Cited by 41 publications

(52 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At relaxing conditions ∼75% of the TFs are in the inhibited c-blocked and c-closed structural states, whereas ∼25% TF segments are in the activated c-open state. This is consistent with the diversity of the structural composition of the TF found using biochemical approaches (25) and explains how at low Ca 2+ conditions rigor myosin can bind and activate the TF (26,27). The frequency of the activated c-open state at low Ca 2+ is higher than expected from the kinetic measurements (SI Appendix, Figs.…”

Section: Discussionsupporting

confidence: 73%

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

Risi

Belknap

Heeley

et al. 2018

Biophysical Journal

View full text Add to dashboard Cite

Muscle contraction relies on the interaction of myosin motors with F-actin, which is regulated through a translocation of tropomyosin by the troponin complex in response to Ca 2+ . The current model of muscle regulation holds that at relaxing (low-Ca 2+ ) conditions tropomyosin blocks myosin binding sites on F-actin, whereas at activating (high-Ca 2+ ) conditions tropomyosin translocation only partially exposes myosin binding sites on F-actin so that binding of rigor myosin is required to fully activate the thin filament (TF). Here we used a single-particle approach to helical reconstruction of frozen hydrated native cardiac TFs under relaxing and activating conditions to reveal the azimuthal movement of the tropomyosin on the surface of the native cardiac TF upon Ca 2+ activation. We demonstrate that at either relaxing or activating conditions tropomyosin is not constrained in one structural state, but rather is distributed between three structural positions on the surface of the TF. We show that two of these tropomyosin positions restrain actomyosin interactions, whereas in the third position, which is significantly enhanced at high Ca 2+ , tropomyosin does not block myosin binding sites on F-actin. Our data provide a structural framework for the enhanced activation of the cardiac TF over the skeletal TF by Ca 2+ and lead to a mechanistic model for the regulation of the cardiac TF.thin filament | cardiac muscle regulation | cryoelectron microscopy

show abstract

Section: Discussionsupporting

confidence: 73%

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

Risi

Belknap

Heeley

et al. 2018

Biophysical Journal

View full text Add to dashboard Cite

show abstract

“…For example, the deletion of the inhibitory region from fsTnI drastically impaired its ability to inhibit the actin-activated myosin ATPase activity (28). These interactions hold most of the thin filaments in the B-state at low [Ca 2ϩ ] (5,7,9). With Ca 2ϩ -bound to the regulatory site(s) of TnC, the population of the thin filaments in the B-state decreases and the C-state and the M-state predominate.…”

mentioning

confidence: 99%

“…The three states have been defined to reflect different interactions between actin and the myosin head. The B-state, which the majority of the thin filaments occupy when the cytoplasmic [Ca 2ϩ ] is low and Ca 2ϩ is not bound to the regulatory site(s) on Tn (5,8,9), is stabilized by the interaction between TnI and actin. With Ca 2ϩ binding to the regulatory site(s) of TnC, a hydrophobic patch is exposed in the N-terminal regulatory site of TnC (10, 11).…”

mentioning

confidence: 99%

Increased Ca2+ Affinity of Cardiac Thin Filaments Reconstituted with Cardiomyopathy-related Mutant Cardiac Troponin I

Kobayashi

Solaro

2006

Journal of Biological Chemistry

116

129

View full text Add to dashboard Cite

To understand the molecular mechanisms whereby cardiomyopathy-related cardiac troponin I (cTnI) mutations affect myofilament activity, we have investigated the Ca 2؉ binding properties of various assemblies of the regulatory components that contain one of the cardiomyopahty-related mutant cTnI. Acto-S1 ATPase activities in reconstituted systems were also determined. We investigated R145G and R145W mutations from the inhibitory region and D190H and R192H mutations from the second actin-tropomyosinbinding site. Each of the four mutations sensitized the acto-S1 ATPase to Ca 2؉ . Whereas the mutations from the inhibitory region increased the basal level of ATPase activity, those from the second actin-tropomyosin-binding site did not. The effects on the Ca 2؉ binding properties of the troponin ternary complex and the troponin-tropomyosin complex with one of four mutations were either desensitization or no effect compared with those with wild-type cTnI. All of the mutations, however, affected the Ca 2؉ sensitivities of the reconstituted thin filaments in the same direction as the acto-S1 ATPase activity. Also the thin filaments with one of the mutant cTnIs bound Ca 2؉ with less cooperativity compared with those with wild-type cTnI. These data indicate that the mutations found in the inhibitory region and those from the second actintropomyosin site shift the equilibrium of the states of the thin filaments differently. Moreover, the increased Ca 2؉ bound to myofilaments containing the mutant cTnIs may be an important factor in triggered arrhythmias associated with the cardiomyopathy.In experiments reported here, we have investigated the functional significance of mutations of cardiac troponin I (cTnI) 2 linked to cardiomyopathy. The Ca 2ϩ -dependent interaction of TnI with actin and TnC is one of the most important events in the regulation of striated muscle contraction. Ca 2ϩ binding to troponin C (TnC) triggers a series of conformational transitions among thin filament proteins that activate the thin filament (for review, see Refs. 1-4). A current model for the regulatory mechanism of muscle contraction, originally derived from biochemical analysis, involves three states of the thin filament:blocked (B-state), closed (C-state), and open (M-state) (5-7). The three states have been defined to reflect different interactions between actin and the myosin head. The B-state, which the majority of the thin filaments occupy when the cytoplasmic [Ca 2ϩ ] is low and Ca 2ϩ is not bound to the regulatory site(s) on Tn (5,8,9), is stabilized by the interaction between TnI and actin. With Ca 2ϩ binding to the regulatory site(s) of TnC, a hydrophobic patch is exposed in the N-terminal regulatory site of TnC (10, 11). In the case of cardiac TnC (cTnC), this structural change requires cTnI (12-14). The newly exposed hydrophobic patch interacts with the regulatory region of TnI (12, 15-17) and the C-terminal half of the TnI molecule moves away from actin (18 -22). In the C-state, non-force-generating cross-bridges bind weakly to actin...

show abstract

“…In muscles, troponin I (TnI) is a key element in the protein complex that regulates sliding of thin over thick filaments (Farah and Reinach, 1995;Geeves and Lehrer, 1998;Squire and Morris, 1998;Maytum et al, 2003). Several TnI protein isoforms are generated, either from transcription of independent genes (e.g., vertebrates) or from differential splicing of a single gene primary transcript (e.g., Drosophila).…”

Section: Introductionmentioning

confidence: 99%

Transcription ofDrosophilaTroponin I Gene Is Regulated by Two Conserved, Functionally Identical, Synergistic Elements

Marín

Toledo-Rodriguez

Ferrús

2004

MBoC

View full text Add to dashboard Cite

The Drosophila wings-up A gene encodes Troponin I. Two regions, located upstream of the transcription initiation site (upstream regulatory element) and in the first intron (intron regulatory element), regulate gene expression in specific developmental and muscle type domains. Based on LacZ reporter expression in transgenic lines, upstream regulatory element and intron regulatory element yield identical expression patterns. Both elements are required for full expression levels in vivo as indicated by quantitative reverse transcription-polymerase chain reaction assays. Three myocyte enhancer factor-2 binding sites have been functionally characterized in each regulatory element. Using exon specific probes, we show that transvection is based on transcriptional changes in the homologous chromosome and that Zeste and Suppressor of Zeste 3 gene products act as repressors for wings-up A. Critical regions for transvection and for Zeste effects are defined near the transcription initiation site. After in silico analysis in insects (Anopheles and Drosophila pseudoobscura) and vertebrates (Ratus and Coturnix), the regulatory organization of Drosophila seems to be conserved. Troponin I (TnI) is expressed before muscle progenitors begin to fuse, and sarcomere morphogenesis is affected by TnI depletion as Z discs fail to form, revealing a novel developmental role for the protein or its transcripts. Also, abnormal stoichiometry among TnI isoforms, rather than their absolute levels, seems to cause the functional muscle defects. INTRODUCTIONContractile protein systems are widely represented in most cell types as a force generator device (Davison et al., 2000). In muscles, troponin I (TnI) is a key element in the protein complex that regulates sliding of thin over thick filaments (Farah and Reinach, 1995;Geeves and Lehrer, 1998;Squire and Morris, 1998;Maytum et al., 2003). Several TnI protein isoforms are generated, either from transcription of independent genes (e.g., vertebrates) or from differential splicing of a single gene primary transcript (e.g., Drosophila). Amino acid substitutions in constitutive or alternatively spliced exons in TnI can lead to pathological conditions such as familial hypertrophic cardiomyopathy (Carrier et al., 1993;Coonar and McKenna, 1997) and distal arthrogryposis (Sung et al., 2003), due to abnormal interactions with other sarcomere components. Also, TnI is a relevant indicator of heart failure (Lewinter and Vanburen, 2002) and a potent angiogenesis inhibitor through its interaction with polycystin-2 (Li et al., 2003). The potential applications that this knowledge could provide, however, are handicapped by the scant information on the regulatory mechanisms of TnI gene expression. This issue is particularly relevant in the context of future gene therapy strategies and justifies this in vivo study of the regulatory mechanism of the Drosophila homologue. In addition, this study takes advantage of the fact that TnI in Drosophila is encoded by a single gene, wings up A (wupA), and that isoform replacem...

show abstract

Differential Regulation of the Actomyosin Interaction by Skeletal and Cardiac Troponin Isoforms

Cited by 41 publications

References 43 publications

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

Increased Ca2+ Affinity of Cardiac Thin Filaments Reconstituted with Cardiomyopathy-related Mutant Cardiac Troponin I

Transcription ofDrosophilaTroponin I Gene Is Regulated by Two Conserved, Functionally Identical, Synergistic Elements

Contact Info

Product

Resources

About