Looking for Targets to Restore the Contractile Function in Congenital Myopathy Caused by Gln147Pro Tropomyosin.

Olga E Karpicheva,Armen O Simonyan,Nikita A Rysev,Charles S Redwood,Yurii S Borovikov

doi:10.3390/ijms21207590

Abstract

We have used the technique of polarized microfluorimetry to obtain new insight into the pathogenesis of skeletal muscle disease caused by the Gln147Pro substitution in β-tropomyosin (Tpm2.2). The spatial rearrangements of actin, myosin and tropomyosin in the single muscle fiber containing reconstituted thin filaments were studied during simulation of several stages of ATP hydrolysis cycle. The angular orientation of the fluorescence probes bound to tropomyosin was found to be changed by the substitution and was characteristic for a shift of tropomyosin strands closer to the inner actin domains. It was observed both in the absence and in the presence of troponin, Ca2+ and myosin heads at all simulated stages of the ATPase cycle. The mutant showed higher flexibility. Moreover, the Gln147Pro substitution disrupted the myosin-induced displacement of tropomyosin over actin. The irregular positioning of the mutant tropomyosin caused premature activation of actin monomers and a tendency to increase the number of myosin cross-bridges in a state of strong binding with actin at low Ca2+.

Highlights

Tropomyosin (Tpm) and troponin are key players in thin filament-based regulation of striated muscle contraction [1]
At low Ca2+ concentrations, actin monomers are switched off and Tpm is in the blocked position where it covers the essential regions of myosin-binding sites on actin, anchoring over the outer actin domains in most energetically favorable position with roughly 30 electrostatic interactions with actin [7]
The structural and functional effects of a number of Tpm mutations associated with different variants of congenital myopathy have been investigated previously [29,31,32]

Summary

Introduction

Tropomyosin (Tpm) and troponin are key players in thin filament-based regulation of striated muscle contraction [1] These regulatory components in coordination contribute to the work of actin-myosin complex triggering the force generation and, just as importantly, providing the relaxation. At low Ca2+ concentrations, actin monomers are switched off and Tpm is in the blocked position where it covers the essential regions of myosin-binding sites on actin, anchoring over the outer actin domains in most energetically favorable position with roughly 30 electrostatic interactions with actin [7]. The strong binding of myosin to actin moves Tpm deeper into the actin groove to the open position, most parts of actin monomers are switched-on and stimulate release of ADP and Pi from active site of myosin, significant conformational changes in the myosin head and generation of the power stroke. Tpm takes its position over outer actin domains again, inhibits myosin binding with actin and the cycle resumes

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