Single cardiac ventricular myosins are autonomous motors

• Main Authors: Yihua Wang, Chen-Ching Yuan, Katarzyna Kazmierczak, Danuta Szczesna-Cordary, Thomas P. Burghardt
• Format: Article
• Language: English
• Published: The Royal Society 2018-04-01
• Series: Open Biology
• Subjects: single cardiac myosin mechanics; super-resolution microscopy; ratcheting myosin essential light chain; qdot labelled actin under load; cardiomyopathy-linked mutants
• Online Access: https://royalsocietypublishing.org/doi/pdf/10.1098/rsob.170240

Myosin transduces ATP free energy into mechanical work in muscle. Cardiac muscle has dynamically wide-ranging power demands on the motor as the muscle changes modes in a heartbeat from relaxation, via auxotonic shortening, to isometric contraction. The cardiac power output modulation mechanism is explored in vitro by assessing single cardiac myosin step-size selection versus load. Transgenic mice express human ventricular essential light chain (ELC) in wild- type (WT), or hypertrophic cardiomyopathy-linked mutant forms, A57G or E143K, in a background of mouse α-cardiac myosin heavy chain. Ensemble motility and single myosin mechanical characteristics are consistent with an A57G that impairs ELC N-terminus actin binding and an E143K that impairs lever-arm stability, while both species down-shift average step-size with increasing load. Cardiac myosin in vivo down-shifts velocity/force ratio with increasing load by changed unitary step-size selections. Here, the loaded in vitro single myosin assay indicates quantitative complementarity with the in vivo mechanism. Both have two embedded regulatory transitions, one inhibiting ADP release and a second novel mechanism inhibiting actin detachment via strain on the actin-bound ELC N-terminus. Competing regulators filter unitary step-size selection to control force-velocity modulation without myosin integration into muscle. Cardiac myosin is muscle in a molecule.