Light-induced structural changes in a full-length cyanobacterial phytochrome probed by time-resolved X-ray scattering

Area of Science:

• Biochemistry
• Structural Biology
• Photobiology

Background:

• Phytochromes are crucial photoreceptor proteins that mediate light responses in organisms.
• Their function involves signal transduction from a light-sensing domain to an output domain through conformational changes.
• The precise nature and kinetics of these protein conformational changes during photoconversion are not fully elucidated.

Purpose of the Study:

• To investigate the kinetics of structural changes in a full-length cyanobacterial phytochrome and a truncated variant.
• To determine the timescale of signal transmission from the photosensory to the output domain.
• To establish whether early structural dynamics are influenced by the output domain.

Main Methods:

• Time-resolved X-ray scattering
• Optical spectroscopy
• Comparative analysis of full-length and truncated phytochrome variants

Main Results:

• Microsecond to millisecond timescale X-ray scattering and spectroscopic signals were largely unaffected by the presence of the output domain.
• Significant differences between full-length and truncated proteins emerged on longer timescales, indicating signal transmission time.
• These longer-timescale differences represent substantial quaternary structural motions.

Conclusions:

• The early structural dynamics (µs/ms) of the phytochrome photosensory region are independent of the output domain.
• This independence defines a specific time window for characterizing photoreactions.
• This finding is valuable for optogenetic design, enabling independent engineering of output domains.