Photocycle of Cyanobacteriochrome TePixJ.

Samantha J O Hardman,Derren J Heyes,Nigel S Scrutton,Igor V Sazanovich

doi:10.1021/acs.biochem.0c00382

Abstract

Due to the recent advances in X-ray free electron laser techniques, bilin-containing cyanobacteriochrome photoreceptors have become prime targets for the ever-expanding field of time-resolved structural biology. However, to facilitate these challenging studies, it is essential that the time scales of any structural changes during the photocycles of cyanobacteriochromes be established. Here, we have used visible and infrared transient absorption spectroscopy to probe the photocycle of a model cyanobacteriochrome system, TePixJ. The kinetics span multiple orders of magnitude from picoseconds to seconds. Localized changes in the bilin binding pocket occur in picoseconds to nanoseconds, followed by more large-scale changes in protein structure, including formation and breakage of a second thioether linkage, in microseconds to milliseconds. The characterization of the entire photocycle will provide a vital frame of reference for future time-resolved structural studies of this model photoreceptor.

Highlights

Due to the recent advances in X-ray free electron laser techniques, bilin-containing cyanobacteriochrome photoreceptors have become prime targets for the ever-expanding field of time-resolved structural biology
CBCRs contain a linear bilin chromophore linked to the protein by one or more Cys residues located within a light-sensing domain, known as a GAF domain
It has been found that the wavelength sensitivity of CBCRs can be affected by the exact conformation of each of the rings within the bilin, as well as factors such as protonation and hydration,[8] and even the orientation of the D ring of the bilin cofactor, which changes the conjugation of the ring system.[9]

Summary

Communication appears as though formation of the Cys linkage occurs more

Corresponding Author rapidly than the breakage of this bond during the reverse step.[23]. We have used visible and infrared transient absorption measurements to identify the time scales of intermediate formation in the photoconversions of the CBCR TePixJ (Figure 4). Heyes − Manchester Institute of Biotechnology and Department of Chemistry, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester, Manchester M1 7DN, U.K. Igor V. Further time-resolved studies to probe millisecond to second changes using vibrational (infrared or Raman) spectroscopy or circular dichroism would provide valuable elucidation of any later reaction steps.

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■ REFERENCES