title: Initial steps of signal generation in photoactive yellow protein revealed with femtosecond mid-infrared spectroscopy.
abstract: Photoactive yellow protein (PYP) is a bacterial blue light sensor that induces Halorhodospira halophila to swim away from intense blue light. Light absorption by PYP's intrinsic chromophore, p-coumaric acid, leads to the initiation of a photocycle that comprises several distinct intermediates. Here we describe the initial structural changes of the chromophore and its nearby amino acids, using visible pump/mid-infrared probe spectroscopy. Upon photoexcitation, the trans bands of the chromophore are bleached, and shifts of the phenol ring bands occur. The latter are ascribed to charge translocation, which probably plays an essential role in driving the trans to cis isomerization process. We conclude that breaking of the hydrogen bond of the chromophore's C=O group with amino acid Cys69 and formation of a stable cis ground state occur in approximately 2 ps. Dynamic changes also include rearrangements of the hydrogen-bonding network of the amino acids around the chromophore. Relaxation of the coumaryl tail of the chromophore occurs in 0.9-1 ns, which event we identify with the I(0) to I(1) transition observed in visible spectroscopy.
authors.affiliation: Faculty of Sciences, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands. marloes@nat.vu.nl
authors.forename: Marie Louise
authors.initials: ML
authors.lastname: Groot
authors.forename: Luuk J G W
authors.initials: LJ
authors.lastname: van Wilderen
authors.forename: Delmar S
authors.initials: DS
authors.lastname: Larsen
authors.forename: Michael A
authors.initials: MA
authors.lastname: van der Horst
authors.forename: Ivo H M
authors.initials: IH
authors.lastname: van Stokkum
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: Hellingwerf
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology / Q000528:radiation effects; D001665:Binding Sites; D003373:Coumaric Acids / Q000737:chemistry; D006860:Hydrogen Bonding; D007536:Isomerism; D007700:Kinetics; D008027:Light; D008956:Models, Chemical; D008958:Models, Molecular; D010636:Phenols / Q000737:chemistry; D010777:Photochemistry; D020283:Photoreceptors, Microbial / Q000737:chemistry* / Q000502:physiology / Q000528:radiation effects; D011789:Quantum Theory; D015398:Signal Transduction; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013997:Time Factors
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D003373:Coumaric Acids; D010636:Phenols; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria