Harmonic force spectroscopy measures load-dependent kinetics of individual human b-cardiac myosin molecules

Jongmin Sung (1, 2) , Suman Nag (1) , Kim I. Mortensen (3) , Christian L. Vestergaard (4, 3, 5) , Shirley Sutton (1) , Kathleen Ruppel (1) , Henrik Flyvbjerg (3) , James A Spudich (1)

1 Stanford School of Medicine [Stanford]
2 Stanford University
3 DTU Nanotech
4 CPT - E5 Physique statistique et systèmes complexes
5 CPT - Centre de Physique Théorique - UMR 7332

Molecular motors are responsible for numerous cellular processes from cargo transport to heart contraction. Their interactions with other cellular components are often transient and exhibit kinetics that depend on load. Here, we measure such interactions using 'harmonic force spectroscopy'. In this method, harmonic oscillation of the sample stage of a laser trap immediately, automatically and randomly applies sinusoidally varying loads to a single motor molecule interacting with a single track along which it moves. The experimental protocol and the data analysis are simple, fast and efficient. The protocol accumulates statistics fast enough to deliver single-molecule results from single-molecule experiments. We demonstrate the method's performance by measuring the force-dependent kinetics of individual human b-cardiac myosin molecules interacting with an actin filament at physiological ATP concentration. We show that a molecule's ADP release rate depends exponentially on the applied load, in qualitative agreement with cardiac muscle, which contracts with a velocity inversely proportional to external load.

Domaines: Biophysique [physics.bio-ph]; Analyse de données, Statistiques et Probabilités [physics.data-an]; Biochimie, Biologie Moléculaire

Jongmin Sung, Suman Nag, Kim I. Mortensen, Christian L. Vestergaard, Shirley Sutton, et al.. Harmonic force spectroscopy measures load-dependent kinetics of individual human b-cardiac myosin molecules. Nature Communications, 2015, 6, pp.7931. ⟨10.1038/ncomms8931⟩. ⟨hal-01190174⟩