Class II LitR serves as an effector of "short" LOV-type blue-light photoreceptor in Pseudomonas mendocina

Conserved Signal Transduction Mechanisms and Dark Recovery Kinetic Tuning in the Pseudomonadaceae Short Light, Oxygen, Voltage (LOV) Protein Family

Light-Oxygen-Voltage (LOV) flavoproteins transduce a light signal into variable signaling outputs via a structural rearrangement in the sensory core domain, which is then relayed to fused effector domains via α-helical linker elements. Short LOV proteins from Pseudomonadaceae consist of a LOV sensory core and N- and C-terminal α-helices of variable length, providing a simple model system to study the molecular mechanism of allosteric activation. Here we report the crystal structures of two LOV proteins from Pseudomonas fluorescens - SBW25-LOV in the fully light-adapted state and Pf5-LOV in the dark-state. In a comparative analysis of the Pseudomonadaceae short LOVs, the structures demonstrate light-induced rotation of the core domains and splaying of the proximal A'α and Jα helices in the N and C-termini, highlighting evidence for a conserved signal transduction mechanism. Another distinguishing feature of the Pseudomonadaceae short LOV protein family is their highly variable dark recovery, ranging from seconds to days. Understanding this variability is crucial for tuning the signaling behavior of LOV-based optogenetic tools. At 37 °C, SBW25-LOV and Pf5-LOV exhibit adduct state lifetimes of 1470 min and 3.6 min, respectively. To investigate this remarkable difference in dark recovery rates, we targeted three residues lining the solvent channel entrance to the chromophore pocket where we introduced mutations by exchanging the non-conserved amino acids from SBW25-LOV into Pf5-LOV and vice versa. Dark recovery kinetics of the resulting mutants, as well as MD simulations and solvent cavity calculations on the crystal structures suggest a correlation between solvent accessibility and adduct lifetime.

Light regulation in critical human pathogens of clinical relevance such as Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa

It is now clearly recognized that light modulates the physiology of many bacterial chemotrophs, either directly or indirectly. An interesting case are bacterial pathogens of clinical relevance. This work summarizes, discusses, and provides novel complementary information to what is currently known about light sensing and responses in critical human pathogens such as Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus. These pathogens are associated with severe hospital and community infections difficult to treat due to resistance to multiple drugs. Moreover, light responses in Brucella abortus, an important animal and human pathogen, are also compiled. Evidence recovered so far indicates that light modulates aspects related to pathogenesis, persistence, and antibiotic susceptibility in these pathogens; such as motility, biofilm formation, iron uptake, tolerance to antibiotics, hemolysis and virulence. The pathogens elicit differential responses to light depending likely on their pathophysiology, ability to cause disease and characteristics of the host. The response to light is not restricted to discrete physiological traits but is global. In higher organisms, light provides spatial and temporal information. Then, it is crucial to understand what information light is providing in these bacterial pathogens. Our current hypothesis postulates that light serves as a signal that allows these pathogens to synchronize their behavior to the circadian rhythm of the host, to optimize infection. Advances on the molecular mechanism of light signal transduction and physiological responses to light, as well as in the relation between light and bacterial infection, would not only enlarge our understanding of bacterial pathogenesis but also could potentially provide alternative treatment options for infectious illnesses.