Conserved Phenylalanine Residues Are Required for Blue-Shifting of Cyanobacteriochrome Photoproducts

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• 作者：Nathan C. Rockwell ; Shelley S. Martin ; Alexander G. Gulevich ; J. Clark Lagarias
• 刊名：Biochemistry
• 出版年：2014
• 出版时间：May 20, 2014
• 年：2014
• 卷：53
• 期：19
• 页码：3118-3130
• 全文大小：622K
• 年卷期：v.53,no.19(May 20, 2014)
• ISSN：1520-4995

文摘

Cyanobacteriochromes (CBCRs) are cyanobacterial photosensory proteins distantly related to phytochromes. Both phytochromes and CBCRs reversibly convert between dark-stable and photoproduct states upon photoisomerization of their linear tetrapyrrole (bilin) chromophores. While most phytochromes convert between a red-absorbing dark state and a far-red-absorbing photoproduct, CBCRs exhibit spectral responses spanning the entire near-ultraviolet and visible spectrum. For example, red/green CBCRs such as AnPixJ and NpR6012g4 exhibit a red-absorbing dark state similar to that of phytochrome, but photoconversion yields a green-absorbing photoproduct. 鈥淭eal-DXCF鈥?CBCRs convert from blue- or green-absorbing dark states to yield photoproducts with very narrow absorption in the teal region of the spectrum (approximately 500 nm). The recent determination of a crystal structure of AnPixJ in its red-absorbing dark state led to the proposal that movement of a Trp residue (the 鈥渓id Trp鈥? upon photoconversion would allow solvation of the photoproduct, thereby producing a large blue-shift. We find that substitution of the lid Trp has little effect on the NpR6012g4 photoproduct. Instead, two Phe residues conserved in red/green and teal-DXCF CBCRs are essential for determining photoproduct absorption in both CBCR groups with no significant influence on the dark-adapted state. We propose that these Phe residues constrain chromophore movement after primary photoisomerization. This work supports a trapped鈥搕wist mechanism for generating both red/green and teal-DXCF photoproducts.