Photoreceptor proteins and mechanisms of phototransduction in microorganisms

Research Line: MD.P01.008.001 – Protein structure and dynamics
People: Giovanni Cercignani, Giuliano Colombetti, Francesco LenciSabina Lucia, Roberto Marangoni

Description
The ability to perceive and transduce light stimuli allows different microorganisms to use light as a source of information to modulate and modify their movement according to the ambient lighting conditions, which is in turn a prerequisite for searching and achieving the best survival conditions. Understanding the signal transduction mechanisms requires knowledge of the structures and processes that couple the perception of the different characteristics of the light signal (spectral composition, intensity, direction, degree of polarization) to the behavioral response (alteration of the ciliary or flagellar beat). A first step is therefore the study of the localization and spectroscopic characteristics of endogenous pigments in intact cells. It must then be clarified which are the mechanisms of transduction of the light signal, ie which are the metabolic pathways that starting from the signaling state lead to the regulation of the ciliary or flagellar beat.

Main techniques
Image analysis for the tracking of microorganisms
Spectroscopy: absorption, fluorescence
Traditional and confocal fluorescence microscopy

Current activities
In collaboration with the Center of Membrane, Texas Medical School, recombinant strains of Halobacterium salinarum were obtained in which the photoreceptor sensory proteins, SRI and SRII, are linked to Green Fluorescence Protein (GFP). The idea behind this project is to analyze the obtained recombinants both from a behavioral and structural point of view, using confocal and non confocal microscopy, to prove the existence of an ordered distribution of two-dimensional sensory rhodopsins in the cell membrane and their spatial interaction as a possible modulation step of the photoresponse; the latter is, moreover, suggested by the behavioral data so far acquired on non-recombinant strains.In order to study possible uses of photoreceptor proteins in biotechnological applications we started with Bacteriorodopsin (BR), an intensively studied protein and on which in recent years there is a renewed applicative interest. As a first step, a purification protocol of “purple membranes”, was developed, membranes containing BR, which allows to obtain a high sample yield with much shorter times than the procedures described in the literature.

Keywords: Fotomovimenti, fototrasduzione, protozoi ciliati, archeobatteri, fluorescenza, microscopia confocale.

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