Ubiquitous Structural Signaling in Bacterial Phytochromes

Area of Science:

• Biochemistry
• Structural Biology
• Photobiology

Background:

• Phytochromes are light-sensitive proteins crucial for various biological processes.
• Previous studies utilized biochemical, spectroscopic, and crystallographic methods.
• A direct method to probe global conformational signal propagation in phytochromes was missing.

Purpose of the Study:

• To investigate the global conformational changes in bacterial phytochromes upon light activation.
• To determine if different types of phytochromes share a common signaling mechanism.
• To clarify the role of a conserved histidine in phytochrome photoresponse.

Main Methods:

• Solution X-ray scattering was employed to study protein structure in solution.
• Multiple bacterial phytochrome variants were analyzed.

Main Results:

• Bacterial phytochrome photosensory cores exhibit similar large-scale structural changes upon red-light excitation.
• This structural signaling mechanism is conserved in phytochromes with both ordinary and inverted photocycles.
• A specific conserved histidine residue was found to tune the photoresponse rather than directly propagate the signal.

Conclusions:

• Bacterial phytochromes utilize a conserved mechanism for light-induced signal transduction.
• The study provides new insights into the structure-function relationship of phytochromes.
• The findings refine our understanding of the molecular basis of light perception in these proteins.