Fig. 6.

Effect of double switch mutation D382R/R719D on HMM ATPase kinetics. In all cases, black solid line and filled circles are 2-hep HMM data; Red solid line and empty squares are 25-hep HMM data. a Mant-nucleotide single turnover kinetics for D382R/R719D 2-hep and 25-hep HMM. b Actin-activated ATPase data for D382R/R719D 2-hep and 25-hep HMM. a Shows representative data from one preparation each. Panel b is combined from two independent preparations of HMMs with three experimental replicates for each preparation. Each point is an average with the error bar representing the SEM. c Model of the front-side view of the human β-cardiac myosin IHM (MS03 homology model, downloadable at https://spudlab.stanford.edu/homology-models/)²⁶, with the two S1 heads and the light chains shown as lines, and the S2 tail region represented by sticks. The Arg719 residue (blue) is part of the free head converter (purple) and the Asp382 (red) residue is part of the blocked head PHHIS. The heavy blue curved line indicates the generally positive surface of the free head converter that interacts with the generally negative blocked head PHHIS surface, marked by the heavy red curved line. d The image in c rotated 90° counterclockwise about the vertical axis defining the binding interface. The free head converter-binding interface, shown in vacuum-electrostatics mode in PyMOL, is generally positively charged. e The image in c rotated 90° clockwise about the vertical axis defining the binding interface. The blocked head PHHIS-binding interface, shown in vacuum-electrostatics mode in PyMOL, is generally negatively charged. Source data are provided as a Source Data file