Abstract
As a first step toward freeze-trapping and 3-D modeling of the very
rapid load-induced structural responses of active myosin heads, we
explored the conformational range of longer lasting force-dependent
changes in rigor crossbridges of insect flight muscle (IFM). Rigor
IFM fibers were slam-frozen after ramp stretch (1000 ms) of 1-2\%
and freeze-substituted. Tomograms were calculated from tilt series
of 30 nm longitudinal sections of Araldite-embedded fibers. Modified
procedures of alignment and correspondence analysis grouped self-similar
crossbridge forms into 16 class averages with 4.5 nm resolution,
revealing actin protomers and myosin S2 segments of some crossbridges
for the first time in muscle thin sections. Acto-S1 atomic models
manually fitted to crossbridge density required a range of lever
arm adjustments to match variably distorted rigor crossbridges. Some
lever arms were unchanged compared with low tension rigor, while
others were bent and displaced M-ward by up to 4.5 nm. The average
displacement was 1.6 +/- 1.0 nm. "Map back" images that replaced
each unaveraged 39 nm crossbridge motif by its class average showed
an ordered mix of distorted and unaltered crossbridges distributed
along the 116 nm repeat that reflects differences in rigor myosin
head loading even before stretch.
- 15450296
- animal,
- animals,
- chickens,
- conformation,
- cryoelectron
- diffraction,
- dimerization,
- flight,
- gov't,
- insects,
- mechanical,
- microscopy,
- models,
- molecular
- molecular,
- motors,
- muscle
- myosins,
- non-p.h.s.,
- non-u.s.
- p.h.s.,
- protein
- research
- smooth
- stress,
- structure,
- support,
- synchrotrons,
- tertiary,
- tomography,
- u.s.
- x-ray
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