Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: The case of Euglena gracilis

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• 作者：Raffaella Mercatelli ; Franco Quercioli ; Laura Barsanti ; Valter Evangelista ; Primo Coltelli ; Vincenzo Passarelli ; Anna Maria Frassanito ; Paolo Gualtieri
• 关键词：Euglena gracilis ; Photoreception ; Photoreceptor ; Primary photoevent ; Intramolecular photo-switch ; Intermolecular energy transfer ; Rhodopsin-like proteins ; FLIM ; FRET
• 刊名：Biochemical and Biophysical Research Communications
• 出版年：2009
• 出版时间：24 July 2009
• 年：2009
• 卷：385
• 期：2
• 页码：176-180
• 全文大小：371 K

文摘

In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglena gracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A_498, non fluorescent and B₄₆₂, 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., A₄₉₈ becomes B₄₆₂), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B₄₆₂ form acts as donor for the non-fluorescent A₄₉₈ 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.