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Rotational motion of Ca-ATPase monitored by electron spin echoes
C van der Struijf1, T P Pelupessy, E E van Faassen
1Department of Molecular Biophysics, Debye Research Center, Utrecht, The Netherlands.
Abstract:
Electron spin echoes are used to study the dynamics of different aggregational forms of spin-labeled Ca-ATPase in the sarcoplasmic reticulum membrane. The 2D-ESE measurements are sensitive to motions on the microsecond time scale. The motional information is extracted from the variation of the echo decays across the CW-ESR absorption spectrum. The motional contribution to the decays is described by assuming that the Ca-ATPase molecule is perfectly oriented along the normal to the membrane surface and only undergoes rotational motion about its long axis. The echo-amplitude decays have been evaluated in the time domain by solving the Bloch equations for the stochastic spin Hamiltonian on making use of stochastic trajectories for the orientational behavior of the spin-labeled protein. This approach provides a useful insight into the information provided by the 2D-ESE measurements and affords a direct comparison of the results obtained with different experimental techniques. It is shown that the 2D-ESE technique monitors the orientational motions of dimers or larger aggregates of Ca-ATPase molecules whose rotational correlation times vary between 200 microseconds and 1 ms for the temperature range between 37 and 4 degrees C.
Insights
Electron spin echo (ESE) spectroscopy reveals the microsecond dynamics of spin-labeled Ca-ATPase in membranes. This technique tracks the rotational motion of Ca-ATPase aggregates, offering insights into protein dynamics.
Area of Science:
- Biophysics
- Membrane Protein Dynamics
- Spectroscopy
Background:
- Calcium-dependent ATPase (Ca-ATPase) plays a crucial role in muscle contraction and cellular calcium homeostasis.
- Understanding the dynamics and aggregation states of Ca-ATPase in the sarcoplasmic reticulum membrane is vital for elucidating its function.
- Previous studies have utilized various techniques to probe membrane protein dynamics, but microsecond timescale motions remain challenging to characterize.
Purpose of the Study:
- To investigate the dynamics of different aggregational forms of spin-labeled Ca-ATPase in the sarcoplasmic reticulum membrane.
- To utilize two-dimensional electron spin echo (2D-ESE) spectroscopy to probe microsecond timescale motions.
- To extract motional information from echo decay variations across the continuous-wave electron spin resonance (CW-ESR) spectrum.
Main Methods:
- Employing electron spin echo (ESE) spectroscopy, specifically 2D-ESE measurements, to study spin-labeled Ca-ATPase.
- Analyzing echo decay variations across the CW-ESR absorption spectrum to extract motional information.
- Solving Bloch equations for a stochastic spin Hamiltonian using stochastic trajectories to model protein orientational behavior.
Main Results:
- 2D-ESE measurements are sensitive to motions occurring on the microsecond timescale.
- The study successfully modeled the motional contribution to echo decays by assuming rotational motion about the long axis of Ca-ATPase.
- The 2D-ESE technique was shown to monitor the orientational motions of Ca-ATPase dimers or larger aggregates.
Conclusions:
- 2D-ESE spectroscopy provides valuable insights into the microsecond dynamics of membrane-bound Ca-ATPase.
- Rotational correlation times for Ca-ATPase aggregates were determined to be between 200 microseconds and 1 ms over a temperature range of 4–37°C.
- This approach allows for direct comparison with results from other experimental techniques, validating the findings.