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An Animated Model for Muscle Myosin-Based Motility.
Muscle myosin is a dimer of two identical motor heads that are anchored
to the thick filament (top) by a coiled-coil (gray rod extending to the
upper right). The helical actin filament is shown at the bottom (gray).
Myosin's catalytic core is blue and its mechanical elements (converter,
lever arm helix and surrounding light chains) are colored yellow or red.
In the beginning of the movie, the myosin heads are in the prestroke
ADP-Pi state (yellow) and the catalytic cores bind weakly to actin. Once
a head docks properly onto an actin subunit (green), phosphate (Pi) is
released from the active site. Phosphate release increases the affinity
of the myosin head for actin and swings the converter/lever arm to the
poststroke, ADP state (transition from yellow to red). The swing of the
lever arm moves the actin filament by ~100 Å; the exact distance may vary
from cycle to cycle depending upon the initial prestroke binding configuration
of the myosin on actin. After completing the stroke, ADP dissociates and
ATP binds to the empty active site, which causes the catalytic core to
detach from actin. The lever arm then recocks back to its prestroke state
(transition from red to yellow). The surface features of the myosin head
and the actin filament were rendered from X-ray crystal structures by
Graham Johnson (fiVth media: www.fiVth.com)
using the programs MolView, Strata Studio Pro and Cinema 4D. PDB files used
were ADP-AlF4- smooth
muscle myosin (prestroke, yellow: #1BR2) and nucleotide-free chicken
skeletal myosin (poststroke, red: #2MYS). Transitions between myosin
crystal structure states were performed by computer-coordinated extrapolations
between the known prestroke and poststroke positions.
Contact information:
Ron Vale (vale@phy.ucsf.edu)
Ron Milligan (milligan@scripps.edu)
Graham Johnson (graham@fiVth.com)
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