Photocycle of cyanobacteriochrome TePixJ

Due to the recent advances in X-ray free electron laser techniques the bilin-containing cyanobacteriochrome photoreceptors have become prime targets for the ever expanding field of time-resolved structural biology. However, in order to facilitate these challenging studies it is essential that the timescales of any structural changes during the photocycles of cyanobacteriochromes are 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 picosecond to nanoseconds, followed by more large-scale changes in protein structure, including formation and breakage of a second thioether linkage, in microsecond 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.