Department of Chemistry , University of California, Davis , One Shields Avenue , Davis , California 95616 , United States.
Department of Molecular and Cell Biology , University of California, Davis , One Shields Avenue , Davis , California 95616 , United States.
Biochemistry. 2019 May 7;58(18):2297-2306. doi: 10.1021/acs.biochem.8b01274. Epub 2019 Apr 22.
Cyanobacteriochromes (CBCRs) make up a diverse family of cyanobacterial photoreceptors distantly related to the phytochrome photoreceptors of land plants. At least two lineages of CBCRs have reacquired red-absorbing dark states similar to the phytochrome P resting state but are coupled to green-absorbing light-adapted states rather than the canonical far-red-absorbing light-adapted state. 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 P 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 (P → P) photodynamics and compare the results to temperature-jump cryokinetics measurements. Our studies show that primary isomerization dynamics occur on an ∼10 ps timescale, yet remarkably, the red-shifted primary Lumi-R photoproduct found in all photoactive canonical R/G CBCRs examined to date is extremely short-lived in NpR3784. These results demonstrate that differences in reaction pathways reflect the evolutionary history of R/G CBCRs despite the convergent evolution of their photocycle end products.
蓝藻发色团（CBCRs）构成了一个多样化的蓝藻光受体家族，与陆地植物的光敏色素光受体远缘相关。至少有两个 CBCR 谱系重新获得了类似于光敏色素 P 静息状态的红色吸收暗态，但与经典的远红吸收光适应态相耦合，而不是与经典的远红吸收光适应态相耦合。这样的谱系之一包括经典的红/绿（R/G）CBCRs，其中包括 AnPixJg2（UniProtKB Q8YXY7）和 NpR6012g4（UniProtKB B2IU14），它们已经得到了广泛的研究。在这里，我们研究了 NpR3784（UniProtKB B2J457）的前向 P 光动力学，NpR3784 是第二个 R/G CBCR 亚家族的代表成员。使用宽带瞬态吸收泵探针光谱学，我们描述了主要（100 fs 到 10 ns）和次要（10 ns 到 1 ms）的前向（P→P）光动力学，并将结果与温度跃变低温动力学测量进行了比较。我们的研究表明，主要的异构化动力学发生在大约 10 ps 的时间尺度上，但令人惊讶的是，在迄今为止检查的所有光活性经典 R/G CBCRs 中发现的红色偏移的主要 Lumi-R 光产物在 NpR3784 中非常短暂。这些结果表明，反应途径的差异反映了 R/G CBCRs 的进化历史，尽管它们的光循环终产物经历了趋同进化。
