Abstract
Flavin-based photoreceptor proteins of the LOV (Light, Oxygen, and Voltage) and BLUF (Blue Light sensing Using Flavins) superfamilies are ubiquitous among the three life domains and are essential blue-light sensing systems, not only in plants and algae, but also in prokaryotes. Here we review their biological roles in the prokaryotic world and their evolution pathways. An unexpected large number of bacterial species possess flavin-based photosensors, amongst which are important human and plant pathogens. Still, few cases are reported where the activity of blue-light sensors could be correlated to infectivity and/or has been shown to be involved in the activation of specific genes, resulting in selective growth patterns. Metagenomics and bio-informatic analysis have only recently been initiated, but signatures are beginning to emerge that allow definition of a bona fide LOV or BLUF domain, aiming at better selection criteria for novel blue-light sensors. We also present here, for the first time, the phylogenetic tree for archaeal LOV domains that have reached a statistically significant number but have not at all been investigated thus far.
Highlights
IntroductionA blue-light sensing, flavin-binding receptor (Fl-Blue) that regulates growth patterns and biofilm formation in Listeria monocytogenes (Figure 1a) [1], a single, two-cofactor Fl-Blue that integrates blue-light sensing with the detection of the cellular redox state in the facultative phototroph
We have reported on examples where effects of LOV- and BLUF-domain containing proteins have been identified, either via their physiological properties that are monitored through their signaling domain-in many cases an controllable enzyme activity, or via their impact on their host organisms in case these bacteria are identified as plant or animal/human pathogens
With this algorithm we identified 1390 LOV proteins in 1031 bacterial strains (658 species), 167 archaeal LOV proteins in 86 strains (82 species), and 1705 bacterial BLUF proteins in 1282 strains (453 species; many strains are from E. coli, Acinetobacter and K. pneumoniae)
Summary
A blue-light sensing, flavin-binding receptor (Fl-Blue) that regulates growth patterns and biofilm formation in Listeria monocytogenes (Figure 1a) [1], a single, two-cofactor Fl-Blue that integrates blue-light sensing with the detection of the cellular redox state in the facultative phototroph. 100–110 aa), binding a single flavin chromophore (FMN, flavin mononucleotide, or FAD, flavin adenine dinucleotide) Their photosensing and photoresponding properties, characterized by defined photochemical reactions and spectral features (vide infra) are linked to diverse effector/regulator functions in a large array of different proteins [6]. The reader is referred to recent manuscripts [17,20,21] dealing with key questions, such as: (a) the still controversially discussed photoactivation mechanisms of Cry proteins, relying on antenna chromophores and flavin-centered photoinduced electron transfer reactions; (b) the role of light-activation (e.g., in bacteria, plants, invertebrates) versus light-independent functions in vivo (e.g., in humans); and (c) the long-lasting question of Cry involvement in photo-magnetoreception in migratory birds, via the formation of spin-correlated radical pairs upon blue light excitation. LOV-kinase from P. syringae pv syringae promotes swarming motility by releasing the inhibition mediated by bacteriophytochrome 1 (BphP1) [4]; (d) Three similar BLUF proteins additively regulate the twitching motility of Acinetobacter baylyi in a light-dependent pathway [5]
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