title: Resonance Raman spectroscopy and quantum chemical calculations reveal structural changes in the active site of photoactive yellow protein.
abstract: Photoactive yellow protein (PYP) is a bacterial photoreceptor containing a 4-hydroxycinnamyl chromophore. Photoexcitation of PYP triggers a photocycle that involves at least two intermediate states: an early red-shifted PYP(L) intermediate and a long-lived blue-shifted PYP(M) intermediate. In this study, we have explored the active site structures of these intermediates by resonance Raman spectroscopy. Quantum chemical calculations based on a density functional theory are also performed to simulate the observed spectra. The obtained structure of the chromophore in PYP(L) has cis configuration and no hydrogen bond at the carbonyl oxygen. In PYP(M), the cis chromophore is protonated at the phenolic oxygen and forms the hydrogen bond at the carbonyl group. These results allow us to propose structural changes of the chromophore during the photocycle of PYP. The chromophore photoisomerizes from trans to cis configuration by flipping the carbonyl group to form PYP(L) with minimal perturbation of the tightly packed protein interior. Subsequent conversion to PYP(M) involves protonation on the phenolic oxygen, followed by rotation of the chromophore as a whole. This large motion of the chromophore is potentially correlated with the succeeding global conformational changes in the protein, which ultimately leads to transduction of a biological signal.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan. unno@tagen.tohoku.ac.jp
authors.forename: Masashi
authors.initials: M
authors.lastname: Unno
authors.forename: Masato
authors.initials: M
authors.lastname: Kumauchi
authors.forename: Jun
authors.initials: J
authors.lastname: Sasaki
authors.forename: Fumio
authors.initials: F
authors.lastname: Tokunaga
authors.forename: Seigo
authors.initials: S
authors.lastname: Yamauchi
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D003373:Coumaric Acids / Q000737:chemistry; D003624:Darkness; D020607:Halorhodospira halophila / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D008027:Light; D008956:Models, Chemical; D010777:Photochemistry / Q000379:methods; D020283:Photoreceptors, Microbial; D011422:Propionates; D011522:Protons; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman / Q000379:methods; D014732:Vibration
chemical_list: D001426:Bacterial Proteins; D003373:Coumaric Acids; D020283:Photoreceptors, Microbial; D011422:Propionates; D011522:Protons; C050162:photoactive yellow protein, Bacteria; C495469:p-coumaric acid