X-ray diffraction studies on thermally induced tension generation in rigor muscle

Area of Science:

• Muscle physiology
• Biophysics
• Structural biology

Background:

• Muscle fibers can contract when heated in a nucleotide-free rigor state.
• This rigor contraction shares similarities with calcium-activated muscle contraction.
• The underlying structural mechanisms of rigor contraction are not fully understood.

Purpose of the Study:

• To investigate the structural changes occurring during rigor contraction using X-ray diffraction.
• To compare the structural basis of rigor contraction with calcium-activated contraction.

Main Methods:

• Utilized X-ray diffraction with a two-dimensional image plate to analyze structural changes.
• Employed laser temperature-jump and temperature ramp experiments.
• Measured changes in low-angle X-ray diffraction patterns, including meridional reflections and actin layer-lines.

Main Results:

• Observed reversible changes in X-ray diffraction patterns, including decreased intensity of the 14.5 nm myosin reflection and increased intensity of actin layer-lines (5.9 nm and 5.1 nm).
• A significant decrease in the 14.5 nm myosin reflection intensity correlated with tension generation during temperature ramp heating.
• These changes are comparable to those observed during tension recovery in calcium-activated fibers.

Conclusions:

• Rigor contraction involves structural rearrangements of myosin crossbridges.
• The observed structural changes suggest alterations in crossbridge shape and/or position on actin.
• Findings provide insights into the shared and distinct structural mechanisms of muscle contraction under different conditions.