Light-induced protein structural dynamics in bacteriophytochrome revealed by time-resolved x-ray solution scattering.

Area of Science:

• Biochemistry and Molecular Biology
• Structural Biology
• Photobiology

Background:

• Bacteriophytochromes (BphPs) are red/far-red light photoreceptors controlling diverse biological processes.
• The Pfr-to-Pr photoconversion mechanism in solution remains poorly understood.
• Understanding these dynamics is crucial for deciphering signal transduction in BphPs.

Purpose of the Study:

• To elucidate the structural dynamics of Pfr-to-Pr photoconversion in Bacteriophytochromes.
• To identify intermediate structural states during light-induced transitions.
• To provide mechanistic insights into long-range signal transmission in modular signaling proteins.

Main Methods:

• Time-resolved X-ray solution scattering (TRXSS) was employed to capture light-induced structural changes.
• Kinetic analysis of TRXSS data identified distinct structural species and their interconversion time constants.
• Molecular dynamics simulations were used to analyze quaternary structural rearrangements.

Main Results:

• Three distinct structural species (lumi-F, meta-F, and Pr) were identified during Pfr-to-Pr photoconversion.
• Interconversion occurred with time constants of 95 μs and 21 ms.
• Light activation induced quaternary structural rearrangements from a closed Pfr state to an open Pr state.

Conclusions:

• This study provides the first mechanistic insights into Pfr-to-Pr photoconversion dynamics in solution.
• Revealed structural transitions highlight the role of quaternary rearrangements in signal propagation.
• Findings advance understanding of how Bacteriophytochromes function as modular signaling proteins.