title: Target analysis of primary photoprocesses involved in the oxyblepharismin-binding protein.
abstract: Target analysis is performed on previously published transient absorption spectra of the 200-kDa oxyblepharismin-binding protein (OBIP) thought to trigger the photophobic response of the ciliate Blepharisma japonicum. The OBIP sample is considered as heterogeneous and made of two distinct classes of chromophore-protein complexes. A so-called nonreactive class is seen to be comparable to free oxyblepharismin in organic solution. Another, reactive, class is shown to undergo a fast picosecond photocycle involving the formation in 4 ps of an intermediate state noted Y1. The spectrum associated to Y1 bears striking similarities with that of the oxyblepharismin radical cation. This element favors the hypothesis that an excited-state intermolecular electron-transfer could be the primary step of the sensory transduction chain of B. japonicum. Proton release is also considered as a possible secondary step. These possibilities support the idea that reactive OBIP functions like an electron or proton pump. We alternatively propose a new hypothesis stating that the fast photocycle of reactive OBIP actually does not generate any photoproduct or protein change of conformation but is involved in another biological function. It would act as a kind of solar screen, providing additional protection to the light-adapted form of B. japonicum in case of excessive illumination.
authors.affiliation: Département de Chimie, UMR 8640 CNRS-ENS, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France. Pascal.Plaza@ens.fr
authors.forename: Pascal
authors.initials: P
authors.lastname: Plaza
authors.forename: Mathilde
authors.initials: M
authors.lastname: Mahet
authors.forename: Monique M
authors.initials: MM
authors.lastname: Martin
authors.forename: Giovanni
authors.initials: G
authors.lastname: Checcucci
authors.forename: Francesco
authors.initials: F
authors.lastname: Lenci
mesh_terms: D000818:Animals; D002412:Cations; D002627:Chemistry, Physical / Q000379:methods; D016798:Ciliophora / Q000378:metabolism*; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D004563:Electrochemistry / Q000379:methods; D004583:Electrons; D007700:Kinetics; D008956:Models, Chemical; D008968:Molecular Conformation; D010569:Perylene / Q000031:analogs & derivatives* / Q000737:chemistry; D010777:Photochemistry / Q000379:methods; D011485:Protein Binding; D011487:Protein Conformation; D013053:Spectrophotometry / Q000379:methods
chemical_list: D002412:Cations; C505951:oxyblepharismin; D010569:Perylene; D004121:Dimethyl Sulfoxide