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Lessons from a tarantula: new insights into muscle thick filament and myosin interacting-heads motif structure and function.

ABSTRACT: The tarantula skeletal muscle X-ray diffraction pattern suggested that the myosin heads were helically arranged on the thick filaments. Electron microscopy (EM) of negatively stained relaxed tarantula thick filaments revealed four helices of heads allowing a helical 3D reconstruction. Due to its low resolution (5.0 nm), the unambiguous interpretation of densities of both heads was not possible. A resolution increase up to 2.5 nm, achieved by cryo-EM of frozen-hydrated relaxed thick filaments and an iterative helical real space reconstruction, allowed the resolving of both heads. The two heads, "free" and "blocked", formed an asymmetric structure named the "interacting-heads motif" (IHM) which explained relaxation by self-inhibition of both heads ATPases. This finding made tarantula an exemplar system for thick filament structure and function studies. Heads were shown to be released and disordered by Ca2+-activation through myosin regulatory light chain phosphorylation, leading to EM, small angle X-ray diffraction and scattering, and spectroscopic and biochemical studies of the IHM structure and function. The results from these studies have consequent implications for understanding and explaining myosin super-relaxed state and thick filament activation and regulation. A cooperative phosphorylation mechanism for activation in tarantula skeletal muscle, involving swaying constitutively Ser35 mono-phosphorylated free heads, explains super-relaxation, force potentiation and post-tetanic potentiation through Ser45 mono-phosphorylated blocked heads. Based on this mechanism, we propose a swaying-swinging, tilting crossbridge-sliding filament for tarantula muscle contraction.

SUBMITTER: Alamo L

PROVIDER: S-EPMC5662037 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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Lessons from a tarantula: new insights into muscle thick filament and myosin interacting-heads motif structure and function.

Alamo Lorenzo L Koubassova Natalia N Pinto Antonio A Gillilan Richard R Tsaturyan Andrey A Padrón Raúl R

Biophysical reviews 20170904 5

The tarantula skeletal muscle X-ray diffraction pattern suggested that the myosin heads were helically arranged on the thick filaments. Electron microscopy (EM) of negatively stained relaxed tarantula thick filaments revealed four helices of heads allowing a helical 3D reconstruction. Due to its low resolution (5.0 nm), the unambiguous interpretation of densities of both heads was not possible. A resolution increase up to 2.5 nm, achieved by cryo-EM of frozen-hydrated relaxed thick filaments and ...[more]

PMID: 28871556

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Project description:Phosphorylation of myosin regulatory light chain (RLC) N-terminal extension (NTE) activates myosin in thick filaments. RLC phosphorylation plays a primary regulatory role in smooth muscles and a secondary (modulatory) role in striated muscles, which is regulated by Ca(2+)via TnC/TM on the thin filament. Tarantula striated muscle exhibits both regulatory systems: one switches on/off contraction through thin filament regulation, and another through PKC constitutively Ser35 phosphorylated swaying free heads in the thick filaments that produces quick force on twitches regulated from 0 to 50% and modulation is accomplished recruiting additional force-potentiating free and blocked heads via Ca(2+)4-CaM-MLCK Ser45 phosphorylation. We have used microsecond molecular dynamics (MD) simulations of tarantula RLC NTE to understand the structural basis for phosphorylation-based regulation in tarantula thick filament activation. Trajectory analysis revealed that an inter-domain salt bridge network (R39/E58,E61) facilitates the formation of a stable helix-coil-helix (HCH) motif formed by helices P and A in the unphosphorylated NTE of both myosin heads. Phosphorylation of the blocked head on Ser45 does not induce any substantial structural changes. However, phosphorylation of the free head on Ser35 disrupts this salt bridge network and induces a partial extension of helix P along RLC helix A. While not directly participating in the HCH folding, phosphorylation of Ser35 unlocks a compact structure and allows the NTE to spontaneously undergo coil-helix transitions. The modest structural change induced by the subsequent Ser45 diphosphorylation monophosphorylated Ser35 free head facilitates full helix P extension into a single structurally stable α-helix through a network of intra-domain salt bridges (pS35/R38,R39,R42). We conclude that tarantula thick filament activation is controlled by sequential Ser35-Ser45 phosphorylation via a conserved disorder-to-order transition.

Dataset Information

Lessons from a tarantula: new insights into muscle thick filament and myosin interacting-heads motif structure and function.

Publications

Lessons from a tarantula: new insights into muscle thick filament and myosin interacting-heads motif structure and function.

Similar Datasets

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