A Unified View on Varied Ultrafast Dynamics of the Primary Process in Microbial Rhodopsins
A Unified View on Varied Ultrafast Dynamics of the Primary Process in Microbial Rhodopsins
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DOI：
10.1002/anie.202111930
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发表时间：
2021-11-29
影响因子：
16.6
通讯作者：
Tahara, Tahei
中科院分区：
文献类型：
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作者：
Chang, Chun-Fu;Kuramochi, Hikaru;Tahara, Tahei
质子化视网膜席夫碱（PRSB）发色团的全反式到13顺式光异构化是触发微生物视紫红质各种生物学功能的首要步骤。虽然这种超快的初级过程已经被广泛研究，但人们已经认识到，不同视紫质之间的相关激发态弛豫动力学存在显著差异。为了阐明微生物紫红质主要过程复杂的超快动力学的起源，我们利用飞秒时间分辨吸收（TA）光谱研究了变形紫红质及其D97N突变体和细菌紫红质在宽pH范围内的激发态动力学。TA数据表明，当pH接近PRSB发色团基态反离子残基的pK(a)时，它们的激发态弛豫动力学发生了剧烈变化。这一结果表明，不同紫红质激发态弛豫动力学的差异主要源于基态非均质性（即PRSB对偶质子化/去质子化）的差异。
All-trans to 13-cis photoisomerization of the protonated retinal Schiff base (PRSB) chromophore is the primary step that triggers various biological functions of microbial rhodopsins. While this ultrafast primary process has been extensively studied, it has been recognized that the relevant excited-state relaxation dynamics differ significantly from one rhodopsin to another. To elucidate the origin of the complicated ultrafast dynamics of the primary process in microbial rhodopsins, we studied the excited-state dynamics of proteorhodopsin, its D97N mutant, and bacteriorhodopsin by femtosecond time-resolved absorption (TA) spectroscopy in a wide pH range. The TA data showed that their excited-state relaxation dynamics drastically change when pH approaches the pK(a) of the counterion residue of the PRSB chromophore in the ground state. This result reveals that the varied excited-state relaxation dynamics in different rhodopsins mainly originate from the difference of the ground-state heterogeneity (i.e., protonation/deprotonation of the PRSB counterion).