Characterization of Red/Green Cyanobacteriochrome NpR6012g4 by Solution Nuclear Magnetic Resonance Spectroscopy: A Hydrophobic Pocket for the C15-E,anti Chromophore in the Photoproduct,Biochemistry

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Characterization of Red/Green Cyanobacteriochrome NpR6012g4 by Solution Nuclear Magnetic Resonance Spectroscopy: A Hydrophobic Pocket for the C15-E,anti Chromophore in the Photoproduct
Biochemistry ( IF 2.9 ) Pub Date : 2015-06-05 00:00:00 , DOI: 10.1021/acs.biochem.5b00438
Nathan C. Rockwell ₁ , Shelley S. Martin ₁ , Sunghyuk Lim ₁ , J. Clark Lagarias ₁ , James B. Ames ₁

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Cyanobacteriochromes (CBCRs) are cyanobacterial photosensory proteins distantly related to phytochromes. Like phytochromes, CBCRs reversibly photoconvert between a dark-stable state and a photoproduct via photoisomerization of the 15,16-double bond of their linear tetrapyrrole (bilin) chromophores. CBCRs provide cyanobacteria with complete coverage of the visible spectrum and near-ultraviolet region. One CBCR subfamily, the canonical red/green CBCRs typified by AnPixJg2 and NpR6012g4, can function as sensors of light color or intensity because of their great variation in photoproduct stability. The mechanistic basis for detection of green light by the photoproduct state in this subfamily has proven to be a challenging research topic, with competing hydration and trapped-twist models proposed. Here, we use ¹³C-edited and ¹⁵N-edited ¹H–¹H NOESY solution nuclear magnetic resonance spectroscopy to probe changes in chromophore configuration and protein–chromophore interactions in the NpR6012g4 photocycle. Our results confirm a C15-Z,anti configuration for the red-absorbing dark state and reveal a C15-E,anti configuration for the green-absorbing photoproduct. The photoactive chromophore D-ring is located in a hydrophobic environment in the photoproduct, surrounded by both aliphatic and aromatic residues. Characterization of variant proteins demonstrates that no aliphatic residue is essential for photoproduct tuning. Taken together, our results support the trapped-twist model over the hydration model for the red/green photocycle of NpR6012g4.

中文翻译：

溶液核磁共振波谱表征红色/绿色蓝细菌色素NpR6012g4：光产物中C15- E和反生色团的疏水口袋

蓝细菌色素（CBCRs）是与植物色素远相关的蓝细菌光感蛋白。像植物色素一样，CBCRs通过线性四吡咯（比林）生色团的15,16-双键的光异构化，在暗稳定状态和光产物之间可逆地进行光转换。CBCR为蓝细菌提供了对可见光谱和近紫外线区域的完全覆盖。一个CBCR子家族，以AnPixJg2和NpR6012g4为代表的典型红色/绿色CBCR，由于它们在光产品稳定性方面的巨大差异，因此可以用作光线颜色或强度的传感器。在该亚家族中，通过光产物状态检测绿光的机理基础已被证明是一个具有挑战性的研究课题，提出了竞争性水合作用和加捻扭曲模型。在这里，我们用¹³经过C编辑和¹⁵ N编辑的¹ H– ¹ H NOESY溶液核磁共振波谱，以探测NpR6012g4光循环中发色团构型和蛋白质-发色团相互作用的变化。我们的研究结果确认C15- ž，反为红吸收黑暗状态配置和揭示C15- ê，防绿色吸收光敏产品的配置。光敏发色团D环位于光产品的疏水环境中，被脂肪族和芳香族残基包围。变异蛋白的表征表明，没有脂肪族残基对于光产物调节而言是必不可少的。两者合计，我们的研究结果支持NpR6012g4的红色/绿色光循环的水合模型中的陷阱扭曲模型。

更新日期：2015-06-05

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