Red, Orange, Green: Light- and Temperature-Dependent Color Tuning in a Cyanobacteriochrome.
Biochemistry
; 59(4): 509-519, 2020 02 04.
Article
en En
| MEDLINE
| ID: mdl-31840994
ABSTRACT
Cyanobacteriochromes (CBCRs) are photoreceptor proteins that photoconvert between two parent states and thereby regulate various biological processes. An intriguing property is their variable ultraviolet-visible (UV-vis) absorption that covers the entire spectral range from the far-red to the near-UV region and thus makes CBCRs promising candidates for optogenetic applications. Here, we have studied Slr1393, a CBCR that photoswitches between red- and green-absorbing states (Pr and Pg, respectively). Using UV-vis absorption, fluorescence, and resonance Raman (RR) spectroscopy, a further orange-absorbing state O600 that is in thermal equilibrium with Pr was identified. The different absorption properties of the three states were attributed to the different lengths of the conjugated π-electron system of the phycocyanobilin chromophore. In agreement with available crystal structures and supported by quantum mechanics/molecular mechanics (QM/MM) calculations, the most extended conjugation holds for Pr whereas it is substantially reduced in Pg. Here, the two outer pyrrole rings D and A are twisted out of the plane defined by inner pyrrole rings B and C. For the O600 state, the comparison of the experimental RR spectra with QM/MM-calculated spectra indicates a partially distorted ZZZssa geometry in which ring A is twisted while ring D and the adjacent methine bridge display essentially the same geometry as Pr. The quantitative analysis of temperature-dependent spectra yields an enthalpy barrier of â¼30 kJ/mol for the transition from Pr to O600. This reaction is associated with the movement of a conserved tryptophan residue from the chromophore binding pocket to a solvent-exposed position.
Texto completo:
1
Colección:
01-internacional
Banco de datos:
MEDLINE
Asunto principal:
Ficocianina
/
Fotorreceptores Microbianos
/
Synechocystis
/
Ficobilinas
Tipo de estudio:
Prognostic_studies
Idioma:
En
Revista:
Biochemistry
Año:
2020
Tipo del documento:
Article
País de afiliación:
Alemania