The actin ‘A‐triad's’ role in contractile regulation in health and disease

Schmidt, William M.; Cammarato, Anthony

doi:10.1113/jp276741

Cited by 10 publications

(9 citation statements)

References 112 publications

(146 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…end-to-end overlap, and its surrounding regions, to their oppositely charged binding partners along adjacent actin protomers (16). Precise TNT1−Tpm coupling may thereby, at least in part, account for the enhanced affinity of Tpm for F-actin (18,(23)(24)(25).…”

Section: Discussionmentioning

confidence: 99%

“…No matter its primacy, this switch is considered insufficient for contractile activation; actions of myosin cross-bridges are also required. The switch is also insufficient for inhibition, which requires other features of Tn, Tpm, and actin (9,(12)(13)(14)(15)(16)(17). In particular, the N-terminal half of TnT, otherwise known as TNT1, may play a role in relaxation, to a degree that is an open subject of investigation.…”

mentioning

confidence: 99%

See 1 more Smart Citation

TNNT2 mutations in the tropomyosin binding region of TNT1 disrupt its role in contractile inhibition and stimulate cardiac dysfunction

Madan

Viswanathan

Woulfe

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

View full text Add to dashboard Cite

Muscle contraction is regulated by the movement of end-to-end-linked troponin−tropomyosin complexes over the thin filament surface, which uncovers or blocks myosin binding sites along F-actin. The N-terminal half of troponin T (TnT), TNT1, independently promotes tropomyosin-based, steric inhibition of acto-myosin associations, in vitro. Recent structural models additionally suggest TNT1 may restrain the uniform, regulatory translocation of tropomyosin. Therefore, TnT potentially contributes to striated muscle relaxation; however, the in vivo functional relevance and molecular basis of this noncanonical role remain unclear. Impaired relaxation is a hallmark of hypertrophic and restrictive cardiomyopathies (HCM and RCM). Investigating the effects of cardiomyopathy-causing mutations could help clarify TNT1’s enigmatic inhibitory property. We tested the hypothesis that coupling of TNT1 with tropomyosin’s end-to-end overlap region helps anchor tropomyosin to an inhibitory position on F-actin, where it deters myosin binding at rest, and that, correspondingly, cross-bridge cycling is defectively suppressed under diastolic/low Ca2+ conditions in the presence of HCM/RCM lesions. The impact of TNT1 mutations on Drosophila cardiac performance, rat myofibrillar and cardiomyocyte properties, and human TNT1’s propensity to inhibit myosin-driven, F-actin−tropomyosin motility were evaluated. Our data collectively demonstrate that removing conserved, charged residues in TNT1’s tropomyosin-binding domain impairs TnT’s contribution to inhibitory tropomyosin positioning and relaxation. Thus, TNT1 may modulate acto-myosin activity by optimizing F-actin−tropomyosin interfacial contacts and by binding to actin, which restrict tropomyosin’s movement to activating configurations. HCM/RCM mutations, therefore, highlight TNT1’s essential role in contractile regulation by diminishing its tropomyosin-anchoring effects, potentially serving as the initial trigger of pathology in our animal models and humans.

show abstract

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

TNNT2 mutations in the tropomyosin binding region of TNT1 disrupt its role in contractile inhibition and stimulate cardiac dysfunction

Madan

Viswanathan

Woulfe

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

View full text Add to dashboard Cite

show abstract

“…K326 and K328 of actin are predicted to form highly-favorable electrostatic contacts with Tpm and stabilize its native inhibitory configuration (12, 15, 17-19, 25, 26). These associations dominate the computed Factin-Tpm interaction energy landscape and, together with TnI-actin interactions, are essential for establishing the B-state (5,12,15,22,27). Modification or mutation of K326 or K328 on actin, or residues in their vicinity, have been shown to alter contractile regulation and induce cardiac and skeletal myopathies (21,22,(28)(29)(30).…”

Section: Introductionmentioning

confidence: 99%

Lysine acetylation of F-actin decreases tropomyosin-based inhibition of actomyosin activity

Schmidt

Madan

Foster

et al. 2020

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

Recent proteomics studies of vertebrate striated muscle have identified lysine acetylation at several sites on actin. Acetylation is a reversible post-translational modification (PTM) that neutralizes lysine’s positive charge. Actin’s positively charged residues, particularly K326 and K328, are predicted to form several, critical electrostatic interactions with tropomyosin (Tpm) that promote its binding and bias Tpm to an azimuthal location where it impedes myosin attachment. The troponin (Tn) complex also influences Tpm’s position along filamentous (F-) actin as a function of Ca2+ to regulate exposure of myosin-binding sites and, thus, myosin cross-bridge recruitment and force production. Interestingly, K326 and K328 on sarcomeric actin are among the documented acetylated residues. Using an acetic anhydride-based labeling approach, we showed that excessive, non-specific actin acetylation did not disrupt characteristic F-actin-Tpm binding. However, it significantly reduced Tpm-mediated inhibition of myosin attachment as reflected by increased F-actin-Tpm motility that persisted in the presence of Tn and submaximal Ca2+. Furthermore, decreasing the extent of chemical acetylation, to presumptively target highly-reactive K326 and K328, also resulted in less inhibited F-actin-Tpm, implying that modifying these residues only, influences Tpm’s location and, potentially, thin filament regulation. To unequivocally determine the residue-specific consequences of acetylation on Tn-Tpm-based regulation of actomyosin activity, we assessed the effects of K326Q and K328Q Ac-mimetic actin on Ca2+-dependent, in vitro motility parameters of reconstituted thin filaments (RTFs). Incorporation of K328Q actin significantly enhanced Ca2+ sensitivity of activation relative to control. Together our findings suggest that actin acetylation, particularly K328, modulates muscle contraction via disrupting inhibitory Tpm positioning.

show abstract

“…Mutations and modifications to residues in this region have been shown to alter function by either stabilizing or de-stabilizing the A-state [47]. We propose that MG forms an irreversible glycation modification on K291 residue in the A-triad, changing the allosteric interactions between actin and tropomyosin to stabilize the blocked state of tropomyosin and therefore reduce K B and myofilament calcium sensitivity (Supplemental Figure 5).…”

Section: Discussionmentioning

confidence: 93%

Myofilament Glycation in Diabetes Reduces Contractility by Inhibiting Tropomyosin Movement, is Rescued by cMyBPC Domains

Papadaki

Kampaengsri

Barrick

et al. 2021

Preprint

View full text Add to dashboard Cite

Diabetes doubles the risk of developing heart failure (HF). As the prevalence of diabetes grows, so will HF unless the mechanisms connecting these diseases can be identified. Methylglyoxal (MG) is a glycolysis by-product that forms irreversible modifications on lysine and arginine, called glycation. We previously found that myofilament MG glycation causes sarcomere contractile dysfunction and is increased in patients with diabetes and HF. The aim of this study was to discover the molecular mechanisms by which MG glycation of myofilament proteins cause sarcomere dysfunction and to identify therapeutic avenues to compensate. In humans with type 2 diabetes without HF, we found increased glycation of sarcomeric actin compared to non-diabetics and it correlated with decreased calcium sensitivity. Depressed calcium sensitivity is pathogenic for HF, therefore myofilament glycation represents a promising therapeutic target to inhibit the development of HF in diabetics. To identify possible therapeutic targets, we further defined the molecular actions of myofilament glycation. Skinned myocytes exposed to 100 μM MG exhibited decreased calcium sensitivity, maximal calcium-activated force, and crossbridge kinetics. Replicating MG’s functional affects using a computer simulation of sarcomere function predicted simultaneous decreases in tropomyosin’s blocked-to-closed rate transition and crossbridge duty cycle were consistent with all experimental findings. Stopped-flow experiments and ATPase activity confirmed MG decreased the blocked-to-closed transition rate. Currently, no therapeutics target tropomyosin, so as proof-of-principal, we used a n-terminal peptide of myosin-binding protein C, previously shown to alter tropomyosin’s position on actin. C0C2 completely rescued MG-induced calcium desensitization, suggesting a possible treatment for diabetic HF.

show abstract

The actin ‘A‐triad's’ role in contractile regulation in health and disease

Cited by 10 publications

References 112 publications

TNNT2 mutations in the tropomyosin binding region of TNT1 disrupt its role in contractile inhibition and stimulate cardiac dysfunction

TNNT2 mutations in the tropomyosin binding region of TNT1 disrupt its role in contractile inhibition and stimulate cardiac dysfunction

Lysine acetylation of F-actin decreases tropomyosin-based inhibition of actomyosin activity

Myofilament Glycation in Diabetes Reduces Contractility by Inhibiting Tropomyosin Movement, is Rescued by cMyBPC Domains

Contact Info

Product

Resources

About