Conformational change in an engineered biliverdin-binding cyanobacteriochrome during the photoconversion process

Area of Science:

• Biochemistry
• Biophysics
• Molecular Biology

Background:

• Cyanobacteriochromes (CBCRs) are photoreceptors related to phytochromes, featuring diverse GAF domains.
• Biliverdin (BV)-binding CBCR GAF domains are crucial for optogenetics due to BV's properties and far-red light absorption.
• Typical BV-binding CBCR GAF domains undergo reversible photoconversion between distinct states.

Purpose of the Study:

• To elucidate the conformational changes underlying the photoconversion process in BV-binding CBCR GAF domains.
• To investigate potential alterations in oligomeric state, surface charge, and secondary structures during photoconversion.
• To identify the specific regions involved in the conformational dynamics.

Main Methods:

• Biochemical and spectral analyses were employed to study CBCR GAF domain photoconversion.
• Protease digestion combined with mass spectrometry was used to pinpoint conformational change regions.
• Oligomeric state, surface charge, and α-helix structural modifications were assessed.

Main Results:

• No changes in the oligomeric state of the CBCR GAF domains were observed during photoconversion.
• Photoconversion was associated with alterations in surface charge and modifications within α-helix structures.
• Mass spectrometry and protease digestion identified specific regions undergoing conformational changes.

Conclusions:

• The photoconversion of BV-binding CBCR GAF domains involves surface charge and α-helix structural rearrangements, not changes in oligomeric state.
• These findings provide critical insights into the molecular mechanisms of CBCR function.
• The identified conformational changes offer valuable information for the future design and optimization of optogenetic tools.