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Light-Driven Chloride Transport Kinetics of Halorhodopsin.

Hasin Feroz1, Bryan Ferlez2, Cecile Lefoulon3

  • 1Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania.

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|July 19, 2018
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Summary

Researchers precisely measured the chloride transport rate of the light-driven anion pump halorhodopsin from Natronomonas pharaonis (NpHR). This study quantifies NpHR

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Area of Science:

  • Optogenetics
  • Biophysics
  • Membrane protein biophysics

Background:

  • Light-driven ion pumps are crucial for optogenetics.
  • Accurate transport rate measurements are challenging due to difficulties in determining protein concentration and orientation in vitro.
  • Existing transport rate estimates for these pumps vary widely.

Purpose of the Study:

  • To directly quantify the light-driven chloride transport rate of the anion pump halorhodopsin from Natronomonas pharaonis (NpHR).
  • To reconcile existing literature values with new direct measurements.
  • To investigate the photocycle kinetics of NpHR under continuous illumination.

Main Methods:

  • Utilized light-interfaced voltage clamp measurements on NpHR-expressing oocytes.
  • Performed consecutive single-turnover flash experiments.
  • Measured chloride transport rates under defined photon flux.

Main Results:

  • Achieved a direct quantitative measurement of NpHR's light-driven Cl- transport rate at 219 (± 98) Cl-/protein/s for a photon flux of 630 photons/protein/s.
  • Results align with NpHR's reported quantum efficiency of approximately 30%.
  • Demonstrated that NpHR bypasses a previously identified 20 ms rate-limiting step under continuous illumination.

Conclusions:

  • Provides the first direct quantitative measurement of NpHR's chloride transport rate.
  • The findings support the understanding of NpHR's photocycle and its efficiency in light-driven ion transport.
  • Highlights the importance of experimental conditions in characterizing ion pump kinetics.