Long-Distance Protonation-Conformation Coupling in Phytochrome Species

Area of Science:

• Biochemistry
• Molecular Biology
• Photobiology

Background:

• Phytochromes are photoreceptors crucial for light sensing in various organisms.
• Signal transduction involves structural changes in phytochrome domains, linking light absorption to cellular responses.
• Previous studies on Cph1 demonstrated a correlation between chromophore deprotonation and pH-dependent conformational changes.

Purpose of the Study:

• To investigate the relationship between chromophore deprotonation and pH-dependent structural dynamics in the biliverdin-binding phytochrome Agp1.
• To compare Agp1's signaling mechanism with that of the phycocyanobilin-binding phytochrome Cph1.
• To elucidate the role of species-specific factors in phytochrome intramolecular signal transduction.

Main Methods:

• Site-directed fluorescence labeling of cysteine variants in Agp1's photosensory domain (PGP).
• Picosecond time-resolved fluorescence anisotropy measurements at various pH levels.
• Analysis of pH-dependent conformational changes and chromophore deprotonation dynamics.

Main Results:

• Agp1 does not exhibit a direct correlation between biliverdin chromophore deprotonation and pH-induced conformational changes.
• Unlike Cph1, Agp1 shows no long-range effects between its PHY domain and the chromophore's pKa.
• Protein mobility changes in Agp1 are not directly linked to transient chromophore deprotonation events.

Conclusions:

• The correlation between transient chromophore deprotonation and intramolecular signal transduction is not universal across all phytochrome species.
• Agp1's signaling mechanism differs from Cph1, highlighting species-specific adaptations in phytochrome function.
• These findings underscore the diversity of molecular mechanisms underlying light signal perception and transduction in phytochromes.