title: Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: the case of Euglena gracilis.
abstract: In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglenagracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A(498,) non fluorescent and B(462), fluorescent. Our data indicate that the primary photoevent of Euglena photoreception upon photon absorption consists of two contemporaneous different phenomena: an intramolecular photo-switch (i.e., A(498) becomes B(462)), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B(462) form acts as donor for the non-fluorescent A(498) form of the protein nearby, which acts as acceptor. We hypothesize that in nature these phenomena follow each other with a domino progression along the orderly organized and closely packed proteins in the photoreceptor layer(s), modulating the isomeric composition of the photoreceptive protein pool. This mechanism guarantees that few photons are sufficient to produce a signal detectable by the cell.
authors.affiliation: Istituto Sistemi Complessi, CNR, Sesto Fiorentino, Italy.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Mercatelli
authors.forename: Franco
authors.initials: F
authors.lastname: Quercioli
authors.forename: Laura
authors.initials: L
authors.lastname: Barsanti
authors.forename: Valter
authors.initials: V
authors.lastname: Evangelista
authors.forename: Primo
authors.initials: P
authors.lastname: Coltelli
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Passarelli
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Frassanito
authors.forename: Paolo
authors.initials: P
authors.lastname: Gualtieri
mesh_terms: D000818:Animals; D005056:Euglena gracilis / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*