The Effective Conjugation Length Is Responsible for the Red/Green Spectral Tuning in the Cyanobacteriochrome Slr1393g3

• Published in: Angewandte Chemie International Edition Vol. 58; no. 7; pp. 1934 - 1938
• Main Authors: Wiebeler, Christian, Rao, Aditya G., Gärtner, Wolfgang, Schapiro, Igor
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 11.02.2019
• Edition: International ed. in English
• Subjects: Absorption; Chromophores; Conjugation; cyanobacteriochromes; Genetics; hybrid QM/MM; Information processing; Medical imaging; Mutation; Optics; Phycocyanobilin; Phytochromes; Proteins; Quantum mechanics; spectral tuning; tetrapyrroles; Tuning; cyanobacteriochromes; chromophores; spectral tuning; hybrid QM/MM; tetrapyrroles
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201810266

The origin of the spectral shift from a red‐ to a green‐absorbing form in a cyanobacteriochrome, Slr1393g3, was identified by combined quantum mechanics/molecular mechanics simulations. This protein, related to classical phytochromes, carries the open‐chain tetrapyrrole chromophore phycocyanobilin. Our calculations reveal that the effective conjugation length in the chromophore becomes shorter upon conversion from the red to the green form. This is related to the planarity of the entire chromophore. A large distortion was found for the terminal pyrrole rings A and D; however, the D ring contributes more strongly to the photoproduct tuning, despite a larger change in the twist of the A ring. Our findings implicate that the D ring twist can be exploited to regulate the absorption of the photoproduct. Hence, mutations that affect the D ring twist can lead to rational tuning of the photoproduct absorption, allowing the tailoring of cyanobacteriochromes for biotechnological applications such as optogenetics and bioimaging. Color change: The origin of the spectral shift from a red‐ to a green‐absorbing form in the cyanobacteriochrome Slr1393g3 was identified by combined quantum mechanics/molecular mechanics simulations and wave function analysis. The calculations reveal that the effective conjugation length in the chromophore becomes shorter upon conversion from the red to the green form.