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Energy transduction optical sensor in skeletal myosin
Thomas P Burghardt1, Sungjo Park, Wen-Ji Dong
1Department of Biochemistry and Molecular Biology, Mayo Foundation, 200 First Street Southwest, Rochester, Minnesota 55905, USA. burghardt@mayo.edu
Biochemistry
|May 14, 2003
Summary
Skeletal muscle myosin uses ATP to generate force. Its ATP-sensitive tryptophan (AST) acts as an optical sensor, but its signal may stem from ground-state electronic changes, not just excited-state interactions.
Area of Science:
- Biochemistry
- Molecular Biology
- Biophysics
Background:
- Skeletal myosin's cross-bridge is the primary energy transducer in muscle, converting ATP hydrolysis into contractile force.
- The ATP-sensitive tryptophan (AST) residue in myosin functions as an optical sensor, reflecting conformational changes during ATP hydrolysis.
- Understanding AST's fluorescence modulation is key to elucidating myosin's ATP sensitivity and energy transduction mechanism.
Purpose of the Study:
- To investigate the mechanism behind the optical signal generated by myosin's ATP-sensitive tryptophan (AST).
- To explore the role of ground-state electronic effects (hypochromism) versus excited-state interactions in AST's fluorescence modulation.
- To correlate AST signal characteristics with myosin's dynamical protein structure during muscle contraction.
Main Methods:
- Time-resolved fluorescence intensity decay measurements of the single AST residue in native myosin.
- Experimental determination of AST hypochromism.
- Comparison of experimental AST hypochromism with calculations based on crystallographic myosin structures.
Main Results:
- Observed experimental AST hypochromism of approximately 30%.
- Calculated maximum AST hypochromism based on static structures was less than 10%.
- The discrepancy suggests that ground-state hypochromism, influenced by local dynamical structure, significantly contributes to the AST optical signal.
Conclusions:
- The optical signal from myosin's AST may be significantly influenced by ground-state hypochromism, a dynamic structural effect.
- This finding reinterprets the AST signal as a direct reporter of local protein dynamics during energy transduction.
- Further research is needed to fully understand the discrepancy between calculated and experimental hypochromism and its implications for myosin S1 structure.