Picosecond multidimensional fluorescence spectroscopy: a tool to measure real-time protein dynamics during function

Area of Science:

• Biophysics
• Photochemistry
• Membrane Protein Dynamics

Background:

• Time-resolved fluorescence techniques offer insights into membrane protein dynamics.
• Fluorescence lifetime and anisotropy changes can signal alterations in protein structure and environment.

Purpose of the Study:

• To investigate changes in bacteriorhodopsin's first cytoplasmic loop upon light activation.
• To correlate fluorescence decay kinetics with bacteriorhodopsin photocycle events.

Main Methods:

• Utilizing advanced multidimensional time-correlated single photon counting (mdTCSPC).
• Employing site-directed fluorescence labeling with fluorescein on bacteriorhodopsin.
• Exciting fluorescence with a picosecond laser and activating bacteriorhodopsin with a 10 ns laser pulse.

Main Results:

• Observed fluorescence decay changes in the picosecond timescale after light activation.
• Identified two transitions between three intermediate states in the latter part of the photocycle.
• Demonstrated that fluorescence changes are coupled to alterations in the retinal binding pocket.

Conclusions:

• The study successfully monitored picosecond dynamics of bacteriorhodopsin's cytoplasmic loop.
• Reaction intermediates at the protein surface were identified and linked to photocycle kinetics.
• These findings provide a deeper understanding of light-induced conformational changes in bacteriorhodopsin.