Forward Photodynamics of the Noncanonical Red/Green NpR3784 Cyanobacteriochrome from Nostoc punctiforme

Cyanobacteriochromes(CBCRs) make up a diverse family of cyanobacterial photoreceptors distantly related to the phytochromephotoreceptors of land plants. At least two lineages of CBCRs have reacquired red-absorbing dark statessimilar to the phytochromePr resting state but are coupled to green-absorbing light-adaptedstates rather than the canonical far-red-absorbing light-adaptedstate. One such lineage includes the canonical red/green (R/G) CBCRs that includes AnPixJg2 (UniProtKB Q8YXY7) and NpR6012g4 (UniProtKB B2IU14) that have been extensively characterized. Here we examine the forward Pr photodynamics of NpR3784 (UniProtKB B2J457), a representative member of the second R/G CBCR subfamily. Using broadband transient absorption pump–probe spectroscopy, we characterize both primary (100 fs to 10 ns) and secondary (10 ns to 1 ms) forward (Pr → Pg) photodynamics and compare the results to temperature-jump cryokinetics measurements. Our studies show that primary isomerization dynamics occur on an ∼10 ps ...