1,721,074 research outputs found
Flavin-based Blue-light Photosensors: a Photobiophysics Update
No full textThis review deals with the biophysical aspects of flavin-based photosensors, comprising cryptochromes, LOV (Light, Oxygen and Voltage) and BLUF (Blue Light sensing Using FAD) proteins. Special emphasis is given to structural issues, photocycle quantum yields and energetics, mechanism of the lighttriggered reactions, early stages in signal transduction and oligomeric states of the light sensing protein modules. For BLUF
and LOV domains important parallels are emerging, despite their different alpha ⁄ beta fold arrangement, whereas there is increasing evidence for a mechanicistic and functional splitting of the cryptochrome family
Fluorescence and time resolved photoacoustics of hypericin inserted in liposomes: dependence on pigment concentration and bilayer phase
No full textSolvatochromic effects on the energy of visible absorbance
and fluorescence transitions in hypericin have been
studied in organic solutions and in phosphatidylcholine
liposomes, suggesting that the molecule in this last case
is preferentially located in the polar aprotic zone close to
the lipid-water interface. Nonradiative and radiative decays
of the pigment have also been studied, combining
photocalorimetric and fluorescence techniques, as a function
of the pigment concentration in the liposomal phase
and of the gel-to-sol thermotropic transition of the phospholipidic
bilayer. The results show that hypericin can
sense the phase transition by exhibiting a stepwise increasing
of the fluorescence quantum yield; concomitantly
photoacoustic data indicate that in the gel phase,
above a certain concentration of hypericin, clustering of
the pigment promotes the formation of nonradiative
long-lived species, whereas when the bilayer is in the sol
phase ultrafast nonradiative pathways become the main
deactivation channels upon increasing concentration. As
a consequence, as shown by photoacoustic results, the
photosensitized formation of singlet oxygen is prevented
when the local concentration of hypericin in the lipidic
phase is greater than about 30 mM
The Evolution of Flavin-Binding Photoreceptors: An Ancient Chromophore Serving Trendy Blue-Light Sensors
No full textPhotoreceptor flavoproteins of the LOV, BLUF, and cryptochrome
families are ubiquitous among the three domains of life and are configured as UVA/blue-light systems not only in plants—their original arena—but also in prokaryotes and microscopic algae. Here, we review these proteins’ structure and function, their biological roles, and their evolution and impact in the living world, and underline their growing application in biotechnologies. We present novel developments such as the interplay of light and redox stimuli, emerging enzymatic and biological functions, lessons on evolution from picoalgae, metagenomics analysis, and optogenetics applications
BLUE LIGHT PHOTORECEPTORS FROM PLANT SYMBIOTIC BACTERIA
No full textIn recent years novel and largely unforeseen biological photoreceptors have been discovered in many bacteria, in most cases with poorly understood in vivo functions. Bacterial photoreceptors mainly belong to two superfamilies: blue light (BL) sensing LOV proteins and red/far red (R/FR) light sensing bacteriophytochromes (BphP), binding respectively flavin mononucleotide (FMN) and biliverdin-IXa (BV) as chromophores. LOV proteins and phytochromes are also the main photoreceptors of plants, and it is clear that many bacteria that are plant pathogens or symbionts are able to detect the same colors as their natural host. In this paper we will present the biophysical characterization of novel BL receptors from Methylobacterium radiotolerans, a radiation resistant, nitrogen fixing bacterium, able to promote plant growth and grow facultatively on methanol (2). In addition, M. radiotolerans is an opportunistic human pathogen and has a high potential for being employed in soil bioremediation. As other Methylobacteria, M. radiotolerans bears genes for several BphP and BL receptors, that we started to investigate during the last months by means of steady state and time-resolved spectroscopy. In particular we focus here on a LOV protein that show high structural stability and an extremely long photocycle in its wild type form. Sequence analysis revealed some peculiarities with respect to the majority of LOV domains; point mutations evidenced that this M. radiotolerans LOV photoreceptor is a promising candidate for biophysical applications, chiefly as fluorescent reporter and as genetically encoded photosensitizer (3). The possible roles of photoreceptors in the physiology of M. radiotolerans is also discussed, on the basis of bioinformatics analysis
Combined spectroscopic and time-resolved photocalorimetric studies of photosensitizers of biomedical interest
No full textLOV proteins photobiophysics
No full textLOV proteins are UVA/Blue light photoreceptors employing LOV (light, oxygen, voltage) domains as photosensory modules. They are wide spread among plants, fungi, bacteria and archaea. LOV domains are /β folds of ca. 110 amino acids and bear a fully oxidized FMN (flavin mononucleotide) chromophore, non covalently bound in the dark adapted state of the protein. Upon photoexcitation, FMN forms a covalent bond with a nearby cysteine (between the cys-SH group and position 4a of the flavin)during the decay of the FMN triplet state (Figure 1). According to its absorption maximum, the adduct is referred to as LOV390 (Figure 2) and is supposed to be the signaling state in vivo. In most LOV proteins, LOV390 thermally recovers to the dark-adapted state, LOV447. Signal propagation from the LOV core to effector domains or protein partners occur via the antiparallel β-scaffold and helical caps flanking the LOV core (figure 3). The peculiar photobiophysics of LOV proteins can be exploited for advanced biotechnological applications, such as fluorescence imaging, superresolution microscopy and optogenetics (figure 4)
A light life together: photosensing in the plant microbiota
Full text linkBacteria and fungi of the plant microbiota can be phytopathogens, parasites or symbionts that establish mutually advantageous relationships with plants. They are often rich in photoreceptors for UVA–Visible light, and in many cases, they exhibit light regulation of growth patterns, infectivity or virulence, reproductive traits, and production of pigments and of metabolites. In addition to the light-driven effects, often demonstrated via the generation of photoreceptor gene knock-outs, microbial photoreceptors can exert effects also in the dark. Interestingly, some fungi switch their attitude towards plants in dependence of illumination or dark conditions in as much as they may be symbiotic or pathogenic. This review summarizes the current knowledge about the roles of light and photoreceptors in plant-associated bacteria and fungi aiming at the identification of common traits and general working ideas. Still, reports on light-driven infection of plants are often restricted to the description of macroscopically observable phenomena, whereas detailed information on the molecular level, e.g., protein–protein interaction during signal transduction or induction mechanisms of infectivity/virulence initiation remains sparse. As it becomes apparent from still only few molecular studies, photoreceptors, often from the red- and the blue light sensitive groups interact and mutually modulate their individual effects. The topic is of great relevance, even in economic terms, referring to plant-pathogen or plant-symbionts interactions, considering the increasing usage of artificial illumination in greenhouses, the possible light-regulation of the synthesis of plant-growth stimulating substances or herbicides by certain symbionts, and the biocontrol of pests by selected fungi and bacteria in a sustainable agriculture
Photofunctional proteins: how nature keeps the laboratories updated about light and life
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