Ultrafast infrared spectroscopy reveals a key step for successful entry into the photocycle for photoactive yellow protein.
Proc Natl Acad Sci U S A
; 103(41): 15050-5, 2006 Oct 10.
Article
in En
| MEDLINE
| ID: mdl-17015839
ABSTRACT
Photoactive proteins such as PYP (photoactive yellow protein) are generally accepted as model systems for studying protein signal state formation. PYP is a blue-light sensor from the bacterium Halorhodospira halophila. The formation of PYP's signaling state is initiated by trans-cis isomerization of the p-coumaric acid chromophore upon the absorption of light. The quantum yield of signaling state formation is approximately 0.3. Using femtosecond visible pump/mid-IR probe spectroscopy, we investigated the structure of the very short-lived ground state intermediate (GSI) that results from an unsuccessful attempt to enter the photocycle. This intermediate and the first stable GSI on pathway into the photocycle, I0, both have a mid-IR difference spectrum that is characteristic of a cis isomer, but only the I0 intermediate has a chromophore with a broken hydrogen bond with the backbone N atom of Cys-69. We suggest, therefore, that breaking this hydrogen bond is decisive for a successful entry into the photocycle. The chromophore also engages in a hydrogen-bonding network by means of its phenolate group with residues Tyr-42 and Glu-46. We have investigated the role of this hydrogen bond by exchanging the H bond-donating residue Glu-46 with the weaker H bond-donating glutamine (i.e., Gln-46). We have observed that this mutant exhibits virtually identical kinetics and product yields as WT PYP, even though during the I0-to-I1 transition, on the 800-ps time scale, the hydrogen bond of the chromophore with Gln-46 is broken, whereas this hydrogen bond remains intact with Glu-46.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Bacterial Proteins
/
Photoreceptors, Microbial
Type of study:
Prognostic_studies
Language:
En
Journal:
Proc Natl Acad Sci U S A
Year:
2006
Document type:
Article
Affiliation country:
Países Bajos