Due to their compact size, modularity and deep penetration of far-red light into mammalian tissues, bilin-based far-red cyanobacterichromes (FR-CBCRs) are of great interest in optogenetics and biomedical applications. We have recently reported the crystal structure of a representative far-red CBCR from Anabena cylindrica, which has revealed an atypical all-Z,syn bilin conformation in the far-red absorbing (Pfr) state. This bilin-based far-red photoreceptor undergoes reversible photoconversion between the Pfr and orange-absorbing (Po) state. To elucidate the molecular mechanism underlying the Pfr/Po photoconversion, we have conducted spectroscopic and dynamic crystallography experiments to capture light-induced structural changes in the photoactive crystals of the isolated photosensory domain of far-red CBCR. We expect to address the following important questions: 1) How does the all-Z,syn bilin chromophore undergo the 15Z/15E photoisomerization in a confined chromophore binding pocket? 2) how does the local signals initiated in the chromophore alter the protein structural changes? We have also engineered a chimeric photoreceptor (denoted FRHK) in which far-red CBCR is covalently coupled to a histidine kinase and a response regulator. Our kinase assays and size exclusion chromatography have shown that the kinase activity of FRHK is upregulated by far-red light illumination, and the kinase activation involves global protein structural changes. These results on far-red CBCR and our progress towards the structural dissection of the allosteric activation in FRHK will be presented.

Molecular mechanisms of photoconversion and kinase activation in a far-red photoreceptor

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.