title: Bifurcation in the Ultrafast Dynamics of the Photoactive Yellow Proteins from Leptospira biflexa and Halorhodospira halophila.
abstract: We explored the photoisomerization mechanisms in novel homologues of photoactive yellow protein (PYP) from Leptospira biflexa (Lbif) to identify conserved features and functional diversity in the primary photochemistry of this family of photoreceptors. In close agreement with the prototypical PYP from Halorhodospira halophila (Hhal), we observe excited-state absorbance near 375 nm and stimulated emission near 500 nm, with triphasic excited-state decay. While the excited-state decay for Lbif PYP is the slowest among those of known PYPs due to the redistribution of the amplitudes of the three decay components, the quantum yield for productive photocycle entry is very similar to that of Hhal PYP. Pro68 is highly conserved in PYPs and is important for the high photochemical quantum yield in Hhal PYP, but this residue is Ile in wild-type Lbif PYP. The level of photoproduct formation is slightly increased in I68P Lbif PYP, indicating that this residue regulates the photochemical quantum yield in the entire PYP family. Lbif PYP also exhibited a blue-shifted photoproduct previously undiscovered in ultrafast studies of PYP, which we have named pUV. We posit that pUV is a detour in the PYP photocycle with a twisted protonated pCAH configuration. Cryokinetic experiments with Hhal PYP confirmed the presence of pUV, but the population of this state in room-temperature ultrafast experiments is very small. These results resolve the long-standing inconsistency in the literature regarding the existence of a bifurcation in the room-temperature photocycle of PYP.
authors.affiliation: Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States.
authors.forename: L Tyler
authors.initials: LT
authors.lastname: Mix
authors.affiliation: Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States.
authors.forename: Julia
authors.initials: J
authors.lastname: Kirpich
authors.affiliation: Department of Microbiology and Molecular Genetics, Oklahoma State University , Stillwater, Oklahoma 74078, United States.
authors.forename: Masato
authors.initials: M
authors.lastname: Kumauchi
authors.affiliation: Department of Microbiology and Molecular Genetics, Oklahoma State University , Stillwater, Oklahoma 74078, United States.
authors.forename: Jie
authors.initials: J
authors.lastname: Ren
authors.affiliation: Faculty of Physics, Laser Research Centre, Vilnius University , Sauletekio 10, LT-10233 Vilnius, Lithuania.
authors.forename: Mikas
authors.initials: M
authors.lastname: Vengris
authors.affiliation: Department of Microbiology and Molecular Genetics, Oklahoma State University , Stillwater, Oklahoma 74078, United States.
authors.forename: Wouter D
authors.initials: WD
authors.lastname: Hoff
authors.affiliation: Department of Chemistry, University of California, Davis , One Shields Avenue, Davis, California 95616, United States.
authors.forename: Delmar S
authors.initials: DS
authors.lastname: Larsen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D020607:Halorhodospira halophila / Q000737:chemistry*; D006860:Hydrogen Bonding; D007919:Leptospira / Q000737:chemistry*; D020283:Photoreceptors, Microbial / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria