King's College London

Research portal

Myosin motors that cannot bind actin leave their folded OFF state on activation of skeletal muscle

Research output: Contribution to journalArticlepeer-review

Massimo Reconditi, Elisabetta Brunello, Luca Fusi, Marco Linari, Vincenzo Lombardi, Malcolm Irving, Gabriella Piazzesi

Original languageEnglish
Article numbere202112896
JournalJournal of General Physiology
Volume153
Issue number11
Early online date20 Oct 2021
DOIs
E-pub ahead of print20 Oct 2021
Published1 Nov 2021

Bibliographical note

Funding Information: Henk L. Granzier served as editor. We thank European Synchrotron Radiation Facility (ESRF) for provision of synchrotron beamtime, Mario Dolfi, the staff of the mechanical workshop of the Department of Physics and Astronomy (University of Florence), and Jacques Gorini (ESRF) for electronic and mechanical engineering support. This work and some investigators were supported by Fondo per gli Investimenti della Ricerca di Base (Futuro in Ricerca project RBFR08JAMZ to E. Brunello, Italy); Progetti di Rilevante Interesse Nazionale-Ministero dell?Istruzione, dell?Universit? e della Ricerca (PRIN-MIUR), and Telethon (Italy); Fondazione Cassa di Risparmio di Firenze (2016-2018; Italy); UK Medical Research Council (grant MR/M026655/1); and the ESRF. E. Brunello was funded by a British Heart Foundation Intermediate Basic Science Research Fellowship FS/17/3/32604. L. Fusi was funded by a Sir Henry Dale Fellowship awarded by the Wellcome Trust and the Royal Society (fellowship 210464/Z/18/Z). Funding Information: This work and some investigators were supported by Fondo per gli Investimenti della Ricerca di Base (Futuro in Ricerca project RBFR08JAMZ to E. Brunello, Italy); Progetti di Rilevante Interesse Nazionale-Ministero dell’Istruzione, dell’Università e della Ricerca (PRIN-MIUR), and Telethon (Italy); Fondazione Cassa di Risparmio di Firenze (2016-2018; Italy); UK Medical Research Council (grant MR/M026655/1); and the ESRF. E. Brunello was funded by a British Heart Foundation Intermediate Basic Science Research Fellowship FS/17/3/32604. L. Fusi was funded by a Sir Henry Dale Fellowship awarded by the Wellcome Trust and the Royal Society (fellowship 210464/Z/18/Z). The authors declare no competing financial interests. Publisher Copyright: © 2021 Reconditi et al.

King's Authors

Abstract

The myosin motors in resting skeletal muscle are folded back against their tails in the thick filament in a conformation that makes them unavailable for binding to actin. When muscles are activated, calcium binding to troponin leads to a rapid change in the structure of the actin-containing thin filaments that uncovers the myosin binding sites on actin. Almost as quickly, myosin motors leave the folded state and move away from the surface of the thick filament. To test whether motor unfolding is triggered by the availability of nearby actin binding sites, we measured changes in the x-ray reflections that report motor conformation when muscles are activated at longer sarcomere length, so that part of the thick filaments no longer overlaps with thin filaments. We found that the intensity of the M3 reflection from the axial repeat of the motors along the thick filaments declines almost linearly with increasing sarcomere length up to 2.8 µm, as expected if motors in the nonoverlap zone had left the folded state and become relatively disordered. In a recent article in JGP, Squire and Knupp challenged this interpretation of the data. We show here that their analysis is based on an incorrect assumption about how the interference subpeaks of the M3 reflection were reported in our previous paper. We extend previous models of mass distribution along the filaments to show that the sarcomere length dependence of the M3 reflection is consistent with <10% of no-overlap motors remaining in the folded conformation during active contraction, confirming our previous conclusion that unfolding of myosin motors on muscle activation is not due to the availability of local actin binding sites.

View graph of relations

© 2020 King's College London | Strand | London WC2R 2LS | England | United Kingdom | Tel +44 (0)20 7836 5454