Phytochromes are widespread red/far-red photosensory proteins well known as critical regulators of photomorphogenesis in plants. Cyanobacteriochrome (CBCR) is phytochrome-related photoreceptors with diverse photosensitivities spanning the entire visible spectrum with 5 different classes to date. Transient absorption spectroscopy on various phytochromes and CBCRs exhibits very diverse excited-state lifetimes and primary photoproduct quantum yields despite utilizing the same phycocyanobilin chromophore. Understanding molecular mechanism of the protein environment modulation of photoactivities can illuminate engineering principles in constructing phytochrome-based fluorescent and optogenetic probes. Cyanobacterial phytochrome Cph1 exhibits low quantum yield of 15 %. Exploiting ultrafast wavelength- and temperature-dependent transient absorption spectroscopy, we resolved fluorescent and photoactive subpopulations in thermal equilibrium in Cph1. Spectral and kinetic behavior of the fluorescent subpopulation strongly resembles that of the photochemically compromised and highly fluorescent Y176H variant of Cph1. This study thus reveals dynamic inhomogeneity in phytochromes as a basis for protein modulation of its photoactivity. Figure 1. <img src='https://acs-archive-assets2.s3.amazonaws.com/240nm/uploads/37840_bendamustine.jpg' alt='' />

Dynamic inhomogeneity in phytochromes and cyanobacteriochromes

247th National Meeting (2014)

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