A Red/Green Cyanobacteriochrome Sustains Its Color Despite a Change in the Bilin Chromophore鈥檚 Protonation State

详细信息    查看全文

• 作者：Chen Song ; Francisco Velazquez Escobar ; Xiu-Ling Xu ; Rei Narikawa ; Masahiko Ikeuchi ; Friedrich Siebert ; Wolfgang G盲rtner ; J枚rg Matysik ; Peter Hildebrandt
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：September 29, 2015
• 年：2015
• 卷：54
• 期：38
• 页码：5839-5848
• 全文大小：603K
• ISSN：1520-4995

文摘

The second GAF domain of AnPixJ, AnPixJg2, a bilin-binding protein from the cyanobacterium Anabaena PCC 7120, undergoes a photoinduced interconversion between a red-absorbing state, Pr, and a green-absorbing state, Pg. Combining ultraviolet鈥搗is (UV鈥搗is), infrared, resonance Raman (RR), and magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, we have studied this cyanobacteriochrome (CBCR) assembled with phycocyanobilin (PCB) either in vivo or in vitro. In both assembly routes, the spectroscopic data of the Pr state reveal nearly identical chromophore structures with a protonated (cationic) bilin. However, unlike the native (in vivo assembly) Pg photoproduct, in which the bilin retains protonation, the Pg generated from the in vitro-assembled AnPixJg2 harbors a deprotonated (neutral) bilin chromophore at pH 7.8. IR difference spectroscopy further reveals the transfer of a proton from the bilin to a side-chain carboxylate on an amino acid, probably Asp291. Besides the change in protonation state, the bilin structure is very similar in the in vitro- and in vivo-assembled Pg photoproducts. The chromophore of the in vitro Pg becomes protonated when the pH is increased to 10, presumably because of a partial reversal of protein misfolding. Most remarkably, the electronic transitions remain unchanged and are very similar to those of the native Pg. Thus, bilin protonation is not a key parameter for controlling the energies of the electronic transitions in AnPixJg2. Possible alternative molecular mechanisms for color tuning are discussed.