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ON THE COVER
As tropomyosin moves during its regulatory transitions from the blocking B-state (magenta) to the closed C-state (gold) during activation, it pivots about one of the helices in its coiled coil (inset boxes), exposing myosin binding sites on actin (surface) while maintaining key electrostatic interactions with actin (energies per residue shown). Image © Lehman and Rynkiewicz, 2023. https://doi.org/10.1085/jgp.202313387. - PDF Icon PDF LinkTable of Contents
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Research News
Pivoting to a new view of tropomyosin movement
JGP study suggests that tropomyosin regulates the crossbridge cycle in muscle by pivoting around relatively fixed points on actin thin filaments.
Commentary
Super relaxed myosins loosen up to different cues in cardiac and skeletal muscle sarcomeres
Recent papers by Nelson et al. and Pilagov et al. provide important new information on the ever-expanding role of myosin heads in the regulation of contraction.
Reviews
The role of Zn2+ in shaping intracellular Ca2+ dynamics in the heart
In this review, we discuss the role of Zn2+ and zinc transporters in regulating cellular Ca2+ dynamics in cardiac muscle.
Articles
Troponin-I–induced tropomyosin pivoting defines thin-filament function in relaxed and active muscle
Lehman and Rynkiewicz show that, in the absence of Ca2+, troponin-I causes tropomyosin to pivot over relatively fixed points on actin subunits, blocking myosin-head binding sites on actin and thereby causing muscle relaxation.
Remodeled connexin 43 hemichannels alter cardiac excitability and promote arrhythmias
This work demonstrates that the opening of lateralize cardiac connexin-43 hemichannels, in the absence of a cardiac pathology, is still sufficient to alter cardiac membrane excitability and promote arrhythmias upon β-adrenergic cardiac stress.
Molecular rearrangements in S6 during slow inactivation in Shaker-IR potassium channels
Szanto et al. provide data that support the idea that rearrangement of S6, including its rotation, may mediate the communication between the activation gate and the inactivation gate controlling slow inactivation in KV channels.
Communications
Physical activity impacts resting skeletal muscle myosin conformation and lowers its ATP consumption
Lewis et al. investigate how training status influences relaxed myosin conformations known to play a role in skeletal muscle metabolism. Their findings indicate that individuals with moderate activity levels have a shift in the relaxed conformations of their type II myosin molecules, lowering the basal ATP consumption.
Extracellular histone proteins activate P2XR7 channel current
Histone proteins are known to be elevated in circulation where they contribute to vascular dysfunction. However, many details regarding the mechanism of action are unknown. Here, the authors show that P2XR7 channel current is activated by extracellularly applied histone proteins in a heterologous expression system.
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