Characterization of red/green cyanobacteriochrome NpR6012g4 by solution NMR spectroscopy: a hydrophobic pocket for the C15-E,anti chromophore in the photoproduct.
Related Articles Characterization of red/green cyanobacteriochrome NpR6012g4 by solution NMR spectroscopy: a hydrophobic pocket for the C15-E,anti chromophore in the photoproduct.
Biochemistry. 2015 May 20;
Authors: Rockwell NC, Martin SS, Lim S, Lagarias JC, Ames JB
Abstract
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. One CBCR subfamily, the canonical red/green CBCRs typified by AnPixJg2 and NpR6012g4, can function as sensors of light color or intensity due to their great variation in photoproduct stability. The mechanistic basis for detection of green light by the photoproduct state in this subfamily has proven a challenging research topic, with competing hydration and trapped-twist models proposed. Here, we use 13C-edited and 15N-edited 1H-1H NOESY solution NMR 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.
PMID: 25989712 [PubMed - as supplied by publisher]
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