The structure of Deinococcus radiodurans transcriptional regulator HucR retold with the urate bound

Structural basis of transcriptional regulation by UrtR in response to uric acid

Uric acid (UA)-responsive transcriptional regulators (UrtRs), which belong to the multiple antibiotic resistance regulator (MarR) superfamily, transcriptionally coordinate virulence and metabolism in bacteria by modulating interactions with operator DNA in response to UA. To elucidate the transcriptional regulatory mechanism of UrtR, we structurally analyzed UrtR proteins, including PecS, MftR, and HucR, alone and in complex with UA or DNA. UrtR contains a dimerization domain (DD) and a winged helix-turn-helix domain (wHTHD) and forms a homodimer primarily via the DD, as observed for other MarR superfamily proteins. However, UrtRs are characterized by a unique N-terminal α-helix, which contributes to dimerization and UA recognition. In the absence of UA, the UrtR dimer symmetrically binds to the operator double-stranded DNA (dsDNA) by inserting its α4 recognition helix and β-stranded wing within the wHTHD into the major and minor grooves of dsDNA, respectively. Upon exposure to UA, UrtR accommodates UA in the intersubunit pocket between the DD and wHTHD. UA binding induces a conformational change in the major groove-binding core element of the UrtR wHTHD, generating a DNA binding-incompatible structure. This local allosteric mechanism of UrtR completely differs from that generally observed in other MarR superfamily members, in which the entire wHTHD undergoes effector-responsive global shifts.

Regulation of bacterial virulence genes by PecS family transcription factors

Bacterial plant pathogens adjust their gene expression programs in response to environmental signals and host-derived compounds. This ensures that virulence genes or genes encoding proteins, which promote bacterial fitness in a host environment, are expressed only when needed. Such regulation is in the purview of transcription factors, many of which belong to the ubiquitous multiple antibiotic resistance regulator (MarR) protein family. PecS proteins constitute a subset of this large protein family. PecS has likely been distributed by horizontal gene transfer, along with the divergently encoded efflux pump PecM, suggesting its integration into existing gene regulatory networks. Here, we discuss the roles of PecS in the regulation of genes associated with virulence and fitness of bacterial plant pathogens. A comparison of phenotypes and differential gene expression associated with the disruption of pecS shows that functional consequences of PecS integration into existing transcriptional networks are highly variable, resulting in distinct PecS regulons. Although PecS universally binds to the pecS-pecM intergenic region to repress the expression of both genes, binding modes differ. A particularly relaxed sequence preference appears to apply for Dickeya dadantii PecS, perhaps to optimize its integration as a global regulator and regulate genes ancestral to the acquisition of pecS-pecM. Even inducing ligands for PecS are not universally conserved. It appears that PecS function has been optimized to match the unique regulatory needs of individual bacterial species and that its roles must be appreciated in the context of the regulatory networks into which it was recruited.

Development of a gene-coded biosensor to establish a high-throughput screening platform for salidroside production

Metabolic engineering reconfigures cellular networks to produce value-added compounds from renewable substrates efficiently. However, identifying strains with desired phenotypes from large libraries through rational or random mutagenesis remains challenging. To overcome this bottleneck, an effective high-throughput screening (HTS) method must be developed to detect and analyze target candidates rapidly. Salidroside is an aromatic compound with broad applications in food, healthcare, medicine, and daily chemicals. However, there currently needs to be HTS methods available to monitor salidroside levels or to screen enzyme variants and strains for high-yield salidroside biosynthesis, which severely limits the development of microbial cell factories capable of efficiently producing salidroside on an industrial scale. This study developed a gene-encoded whole-cell biosensor that is specifically responsive to salidroside. The biosensor was created by screening a site-saturated mutagenic library of uric acid response regulatory protein binding bags. This work demonstrates the feasibility of monitoring metabolic flux with whole-cell biosensors for critical metabolites. It provides a promising tool for building salidroside high-yielding strains for high-throughput screening and metabolic regulation to meet industrial needs.

Gout therapeutics and drug delivery

Gout is a common inflammatory arthritis caused by persistently elevated uric acid levels. With the improvement of people's living standards, the consumption of processed food and the widespread use of drugs that induce elevated uric acid, gout rates are increasing, seriously affecting the human quality of life, and becoming a burden to health systems worldwide. Since the pathological mechanism of gout has been elucidated, there are relatively effective drug treatments in clinical practice. However, due to (bio)pharmaceutical shortcomings of these drugs, such as poor chemical stability and limited ability to target the pathophysiological pathways, traditional drug treatment strategies show low efficacy and safety. In this scenario, drug delivery systems (DDS) design that overcome these drawbacks is urgently called for. In this review, we initially describe the pathological features, the therapeutic targets, and the drugs currently in clinical use and under investigation to treat gout. We also comprehensively summarize recent research efforts utilizing lipid, polymeric and inorganic carriers to develop advanced DDS for improved gout management and therapy.

MarR Family Transcriptional Regulators and Their Roles in Plant-Interacting Bacteria

The relationship between plants and associated soil microorganisms plays a major role in ecosystem functioning. Plant-bacteria interactions involve complex signaling pathways regulating various processes required by bacteria to adapt to their fluctuating environment. The establishment and maintenance of these interactions rely on the ability of the bacteria to sense and respond to biotic and abiotic environmental signals. In this context, MarR family transcriptional regulators can use these signals for transcriptional regulation, which is required to establish adapted responses. MarR-like transcriptional regulators are essential for the regulation of the specialized functions involved in plant-bacteria interactions in response to a wide range of molecules associated with the plant host. The conversion of environmental signals into changes in bacterial physiology and behavior allows the bacteria to colonize the plant and ensure a successful interaction. This review focuses on the mechanisms of plant-signal perception by MarR-like regulators, namely how they (i) allow bacteria to cope with the rhizosphere and plant endosphere, (ii) regulate the beneficial functions of Plant-Growth-Promoting Bacteria and (iii) regulate the virulence of phytopathogenic bacteria.

The Global Regulator MftR Controls Virulence and Siderophore Production in Burkholderia thailandensis

Bacterial pathogens face iron limitation in a host environment. To overcome this challenge, they produce siderophores, small iron-chelating molecules.