Relationship Between Life Satisfaction and Psychological Characteristics Among Community-Dwelling Oldest-old: Focusing on Erikson's Developmental Stages and the Big Five Personality Traits.

OBJECTIVE: To clarify the relationship between life satisfaction and the psychological characteristics of the oldest-old, and explore the factors for achieving mental health and longevity. DESIGN: This cross-sectional study conducted questionnaire surveys and face-to-face interviews as part of a larger prospective cohort study. SETTING: Arakawa Ward, a district in Tokyo, Japan. PARTICIPANTS: A total of 247 oldest-old individuals from two age groups, 85+ (aged 85-87 years) and 95+ (aged 95 years or older). MEASUREMENTS: Life satisfaction was assessed using the Satisfaction with Life Scale (SWLS), developmental stages of the elderly (Erikson's 8th and 9th stages, i.e., ego integrity, and gerotranscendence), and the Big Five personality traits (extraversion, agreeableness, openness, conscientiousness, and neuroticism) using the NEO-Five Factor Inventory. Multiple regression analyses were performed to examine the relationship between the SWLS scores and each assessment, controlling for age, sex, education, activities of daily living, depressive symptoms, and cognitive function. RESULTS: The SWLS scores of 85+ were positively correlated with scores of ego integrity, extraversion, and conscientiousness. Contrastingly, the SWLS scores of 95+ were positively correlated with gerotranscendence scores. CONCLUSIONS: Psychological characteristics associated with the level of life satisfaction among community-dwelling oldest-old individuals were identified, but a causal relationship between these factors and life satisfaction was not established. Ego integrity, extraversion, conscientiousness, and gerotranscendence may be associated with enhanced life satisfaction and mental health in the oldest-old. Further, the factors associated with life satisfaction in the 85+ and 95+ age groups varied, suggesting that life satisfaction among the oldest-old has different foundations in different age groups.

Telepsychiatry versus face-to-face treatment: systematic review and meta-analysis of randomised controlled trials.

BACKGROUND: The COVID-19 pandemic has transformed healthcare significantly and telepsychiatry is now the primary means of treatment in some countries. AIMS: To compare the efficacy of telepsychiatry and face-to-face treatment. METHOD: A comprehensive meta-analysis comparing telepsychiatry with face-to-face treatment for psychiatric disorders. The primary outcome was the mean change in the standard symptom scale scores used for each psychiatric disorder. Secondary outcomes included all meta-analysable outcomes, such as all-cause discontinuation and safety/tolerability. RESULTS: We identified 32 studies (n = 3592 participants) across 11 mental illnesses. Disease-specific analyses showed that telepsychiatry was superior to face-to-face treatment regarding symptom improvement for depressive disorders (k = 6 studies, n = 561; standardised mean difference s.m.d. = -0.325, 95% CI -0.640 to -0.011, P = 0.043), whereas face-to-face treatment was superior to telepsychiatry for eating disorder (k = 1, n = 128; s.m.d. = 0.368, 95% CI 0.018-0.717, P = 0.039). No significant difference was seen between telepsychiatry and face-to-face treatment when all the studies/diagnoses were combined (k = 26, n = 2290; P = 0.248). Telepsychiatry had significantly fewer all-cause discontinuations than face-to-face treatment for mild cognitive impairment (k = 1, n = 61; risk ratio RR = 0.552, 95% CI 0.312-0.975, P = 0.040), whereas the opposite was seen for substance misuse (k = 1, n = 85; RR = 37.41, 95% CI 2.356-594.1, P = 0.010). No significant difference regarding all-cause discontinuation was seen between telepsychiatry and face-to-face treatment when all the studies/diagnoses were combined (k = 27, n = 3341; P = 0.564). CONCLUSIONS: Telepsychiatry achieved a symptom improvement effect for various psychiatric disorders similar to that of face-to-face treatment. However, some superiorities/inferiorities were seen across a few specific psychiatric disorders, suggesting that its efficacy may vary according to disease type.

Language patterns in Japanese patients with Alzheimer disease: A machine learning approach.

AIM: The authors applied natural language processing and machine learning to explore the disease-related language patterns that warrant objective measures for assessing language ability in Japanese patients with Alzheimer disease (AD), while most previous studies have used large publicly available data sets in Euro-American languages. METHODS: The authors obtained 276 speech samples from 42 patients with AD and 52 healthy controls, aged 50 years or older. A natural language processing library for Python was used, spaCy, with an add-on library, GiNZA, which is a Japanese parser based on Universal Dependencies designed to facilitate multilingual parser development. The authors used eXtreme Gradient Boosting for our classification algorithm. Each unit of part-of-speech and dependency was tagged and counted to create features such as tag-frequency and tag-to-tag transition-frequency. Each feature's importance was computed during the 100-fold repeated random subsampling validation and averaged. RESULTS: The model resulted in an accuracy of 0.84 (SD = 0.06), and an area under the curve of 0.90 (SD = 0.03). Among the features that were important for such predictions, seven of the top 10 features were related to part-of-speech, while the remaining three were related to dependency. A box plot analysis demonstrated that the appearance rates of content words-related features were lower among the patients, whereas those with stagnation-related features were higher. CONCLUSION: The current study demonstrated a promising level of accuracy for predicting AD and found the language patterns corresponding to the type of lexical-semantic decline known as 'empty speech', which is regarded as a characteristic of AD.

An immuno-dot blot assay for screening histidine kinase inhibitors.

Two-component signal transduction systems (TCSs), consisting of a histidine kinase (HK) and its cognate response regulator, are ubiquitous among bacteria and are associated with the virulence of pathogens. TCSs are potential targets for alternative antibiotics and antivirulence agents. It is, thus, very important to determine HK activity in bacterial TCSs. Here, we describe an immuno-dot blot assay for the inhibition profiling of HKs using the anti-N3-phosphohistidine antibody. This simple method promises reliable detection of HK activity, and it is likely applicable in high-throughput screening of HK inhibitors.

A Validation Study of the Remotely Administered Montreal Cognitive Assessment Tool in the Elderly Japanese Population.

Background: In an aging society, neuropsychological testing using video teleconferencing (VTC) is increasingly important. Despite the potential benefit of a VTC-administered Montreal Cognitive Assessment Tool (MoCA) to detect cognitive decline, only a limited number of studies have investigated this tool's reliability. Therefore, we aimed to evaluate the reliability of VTC-administered MoCA compared with face-to-face (FTF)-administered MoCA among elderly Japanese participants. Moreover, we examined participants' satisfaction with VTC-administered MoCA. Methods: Participants ≥60 years of age with and without cognitive impairment (i.e., those with mild cognitive impairment [MCI], those with dementia, and healthy controls [HC]) were assessed with VTC- and FTF-administered MoCA at an interval of >2 weeks and <3 months. The order effect (VTC first vs. FTF first) and time effect (first vs. second testing session), as well as several covariates such as age and years of education were controlled. Intraclass correlation coefficients (ICCs) were calculated using a mixed-effects model to assess the agreement between the two (VTC- vs. FTF-administered) groups. Participants' satisfaction with VTC-administered MoCA was examined using a Likert scale asking seven questions. Results: We included 73 participants in the study (36 men; age, 76.3 ± 7.5 years). The ICC for the MoCA total score was high in the entire sample (0.85), whereas ICCs were moderate to high for the subgroups (MCI: 0.82, dementia: 0.82, and HC: 0.53). Furthermore, we found good overall participant satisfaction with VTC-administered MoCA. Discussion: VTC-administered MoCA appears viable as an alternative to FTF-administered MoCA, although further replication studies with larger sample sizes are needed.

Sociopsychological characteristics of late nonagenarians in Japan: the protocol of the Arakawa 95+ study.

AIM: The aim of this study was to examine sociopsychological characteristics of the oldest old in Japan. We conducted a baseline survey of a community-based cohort of persons aged 95 or older. METHODS: Participants were aged 95+ years and resided in Arakawa Ward in Tokyo on 1 January 2016. We mailed a questionnaire to these individuals to assess their physical, mental, and social status. Subsequently, if respondents agreed, we conducted in-home interviews and examined their physical and cognitive function. Also, we mailed non-respondents a simplified version of full questionnaire. Additionally, we examined the basic registered data of the study population and the status of their Long-term Care Insurance. Data at baseline and 1-year follow-up were compared. RESULTS: With regard to Long-term Care Insurance, 423 residents aged 95+ years (78.0%) were on long-term care level, 35 (6.5%) were on support level, and 84 (15.5%) did not require support. At the 1-year follow-up, 275 (50.7%) had the same care level, 107 (19.7%) required a greater level of care, and 131 had died (annual death rate: 24.2%). Compared to the simplified questionnaire group (n = 128) and the full questionnaire-only group (n = 14), a higher proportion of respondents who had completed the full questionnaire and had in-home interviews (n = 26) were men, lived only with a spouse, had higher activities of daily living, and reported more positive feelings and well-being. CONCLUSIONS: In the late nonagenarian population, the annual death rate was high, and care needs increased rapidly. However, some persons maintained the same care level or even showed improvement and successful ageing.

Quantitative monitoring of His and Asp phosphorylation in a bacterial signaling system by using Phos-tag Magenta/Cyan fluorescent dyes.

In the bacterial signaling mechanisms known as two-component systems (TCSs), signals are generally conveyed by means of a His-Asp phosphorelay. Each system consists of a histidine kinase (HK) and its cognate response regulator. Because of the labile nature of phosphorylated His and Asp residues, few approaches are available that permit a quantitative analysis of their phosphorylation status. Here, we show that the Phos-tag dye technology is suitable for the fluorescent detection of His- and Asp-phosphorylated proteins separated by SDS-PAGE. The dynamics of the His-Asp phosphorelay of recombinant EnvZ-OmpR, a TCS derived from Escherichia coli, were examined by SDS-PAGE followed by simple rapid staining with Phos-tag Magenta fluorescent dye. The technique permitted not only the quantitative monitoring of the autophosphorylation reactions of EnvZ and OmpR in the presence of adenosine triphosphate (ATP) or acetyl phosphate, respectively, but also that of the phosphotransfer reaction from EnvZ to OmpR, which occurs within 1 min in the presence of ATP. Furthermore, we demonstrate profiling of waldiomycin, an HK inhibitor, by using the Phos-tag Cyan gel staining. We believe that the Phos-tag dye technology provides a simple and convenient fluorometric approach for screening of HK inhibitors that have potential as new antimicrobial agents.

Identification of an internal cavity in the PhoQ sensor domain for PhoQ activity and SafA-mediated control.

The PhoQ/PhoP two-component signal transduction system is conserved in various Gram-negative bacteria and is often involved in the expression of virulence in pathogens. The small inner membrane protein SafA activates PhoQ in Escherichia coli independently from other known signals that control PhoQ activity. We have previously shown that SafA directly interacts with the sensor domain of the periplasmic region of PhoQ (PhoQ-SD) for activation, and that a D179R mutation in PhoQ-SD attenuates PhoQ activation by SafA. In this study, structural comparison of wild-type PhoQ-SD and D179R revealed a difference in the cavity (SD (sensory domain) pocket) found in the central core of this domain. This was the only structural difference between the two proteins. Site-directed mutagenesis of the residues surrounding the SD pocket has supported the SD pocket as a site involved in PhoQ activity. Furthermore, the SD pocket has also been shown to be involved in SafA-mediated PhoQ control.

Relationships between socio-clinico-demographic factors and global cognitive function in the oldest old living in the Tokyo Metropolitan area: Reanalysis of the Tokyo Oldest Old Survey on Total Health (TOOTH).

BACKGROUND: Despite a steady increase in life expectancy, a few studies have investigated cross-sectional correlates and longitudinal predictors of cognitive function, a core domain of the successful aging, among socio-clinico-demographic factors in the oldest-old exclusively. OBJECTIVES: The aims of this study were to examine socio-clinico-demographic characteristics associated with global cognition and its changes in the oldest-old. METHODS: We reanalyzed a dataset of cognitively preserved community-dwelling subjects aged 85 years and older in the Tokyo Oldest Old Survey on Total Health, a 6-year longitudinal observational study. This study consisted of (1) baseline cross-sectional analyses examining correlates of global cognition (n = 248) among socio-clinico-demographic factors and (2) longitudinal analyses examining baseline predictors for changes of global cognition in 3-year follow-up (n = 195). The Mini-Mental State Examination was used as a screening test to assess global cognition. RESULTS: At baseline, higher weights were related to higher cognitive function in the oldest-old. The baseline predictors of global cognitive decline in 3-year follow-up were higher global cognition, shorter education period, and lower sociocultural activities and lower instrumental activity of daily living, in this order. CONCLUSIONS: The present study suggests that it is crucial to attain higher education during early life and avoid leanness or obesity, participate in sociocultural cognitive activities during late life, and maintain instrumental activity of daily living to preserve optimal cognitive function in the oldest-old, which will facilitate developing prevention strategies for cognitive decline and promoting successful aging in this increasing population.

Identification of the Three Genes Involved in Controlling Production of a Phytotoxin Tropolone in Burkholderia plantarii.

UNLABELLED: Tropolone, a phytotoxin produced by Burkholderia plantarii, causes rice seedling blight. To identify genes involved in tropolone synthesis, we systematically constructed mutations in the genes encoding 55 histidine kinases and 72 response regulators. From the resulting defective strains, we isolated three mutants, KE1, KE2, and KE3, in which tropolone production was repressed. The deleted genes of these mutants were named troR1, troK, and troR2, respectively. The mutant strains did not cause rice seedling blight, and complementation experiments indicated that TroR1, TroK, and TroR2 were involved in the synthesis of tropolone in B. plantarii However, tropolone synthesis was repressed in the TroR1 D52A, TroK H253A, and TroR2 D46A site-directed mutants. These results suggest that the putative sensor kinase (TroK) and two response regulators (TroR1 and TroR2) control the production of tropolone in B. plantarii IMPORTANCE: A two-component system is normally composed of a sensor histidine kinase (HK) and a cognate response regulator (RR) pair. In this study, HK (TroK) and two RRs (TroR1 and TroR2) were found to be involved in controlling tropolone production in B. plantarii These three genes may be part of a bacterial signal transduction network. Such networks are thought to exist in other bacteria to regulate phytotoxin production, as well as environmental adaptation and signal transduction.

Superiority illusion arises from resting-state brain networks modulated by dopamine.

The majority of individuals evaluate themselves as superior to average. This is a cognitive bias known as the "superiority illusion." This illusion helps us to have hope for the future and is deep-rooted in the process of human evolution. In this study, we examined the default states of neural and molecular systems that generate this illusion, using resting-state functional MRI and PET. Resting-state functional connectivity between the frontal cortex and striatum regulated by inhibitory dopaminergic neurotransmission determines individual levels of the superiority illusion. Our findings help elucidate how this key aspect of the human mind is biologically determined, and identify potential molecular and neural targets for treatment for depressive realism.

Honesty mediates the relationship between serotonin and reaction to unfairness.

How does one deal with unfair behaviors? This subject has long been investigated by various disciplines including philosophy, psychology, economics, and biology. However, our reactions to unfairness differ from one individual to another. Experimental economics studies using the ultimatum game (UG), in which players must decide whether to accept or reject fair or unfair offers, have also shown that there are substantial individual differences in reaction to unfairness. However, little is known about psychological as well as neurobiological mechanisms of this observation. We combined a molecular imaging technique, an economics game, and a personality inventory to elucidate the neurobiological mechanism of heterogeneous reactions to unfairness. Contrary to the common belief that aggressive personalities (impulsivity or hostility) are related to the high rejection rate of unfair offers in UG, we found that individuals with apparently peaceful personalities (straightforwardness and trust) rejected more often and were engaged in personally costly forms of retaliation. Furthermore, individuals with a low level of serotonin transporters in the dorsal raphe nucleus (DRN) are honest and trustful, and thus cannot tolerate unfairness, being candid in expressing their frustrations. In other words, higher central serotonin transmission might allow us to behave adroitly and opportunistically, being good at playing games while pursuing self-interest. We provide unique neurobiological evidence to account for individual differences of reaction to unfairness.

Alkali metals in addition to acidic pH activate the EvgS histidine kinase sensor in Escherichia coli.

Two-component signal transduction systems (TCSs) in bacteria perceive environmental stress and transmit the information via phosphorelay to adjust multiple cellular functions for adaptation. The EvgS/EvgA system is a TCS that confers acid resistance to Escherichia coli cells. Activation of the EvgS sensor initiates a cascade of transcription factors, EvgA, YdeO, and GadE, which induce the expression of a large group of acid resistance genes. We searched for signals activating EvgS and found that a high concentration of alkali metals (Na(+), K(+)) in addition to low pH was essential for the activation. EvgS is a histidine kinase, with a large periplasmic sensor region consisting of two tandem PBPb (bacterial periplasmic solute-binding protein) domains at its N terminus. The periplasmic sensor region of EvgS was necessary for EvgS activation, and Leu152, located within the first PBPb domain, was involved in the activation. Furthermore, chimeras of EvgS and PhoQ histidine kinases suggested that alkali metals were perceived at the periplasmic sensor region, whereas the cytoplasmic linker domain, connecting the transmembrane region and the histidine kinase domain, was required for low-pH perception.

Apathy correlates with prefrontal amyloid ß deposition in Alzheimer's disease.

OBJECTIVE: Neuropsychiatric symptoms affect many patients with Alzheimer's disease (AD). ((11)C)Pittsburgh Compound-B (PIB) positron emission tomography (PET) has enabled the in vivo visualisation of brain amyloid-ß (Aß) deposition. This study exploratively investigated the correlation between brain Aß deposition measured by ((11)C)PIB PET and neuropsychiatric symptoms in AD. METHODS: Participants were 28 patients (15 women, 13 men) with PIB-positive AD. Clinical assessments included Mini-Mental State Examination, Clinical Dementia Rating scale, neuropsychiatry inventory (NPI) and frontal assessment battery. All patients underwent three-dimensional T1-weighted MRI and ((11)C)PIB PET. The distribution volume ratio (DVR), an index of ((11)C)PIB retention and, thus, Aß deposition, was estimated voxel by voxel from ((11)C)PIB PET data with partial volume correction. Voxel-based correlation analysis was performed to assess the relationships between DVR and each NPI subscale. Additionally, voxel-based analysis of covariance (ANCOVA) of the DVR images was performed between Patients with AD with and without each neuropsychiatric symptom. Voxel-based morphometry analysis of MRI was also performed. RESULTS: Apathy subscale was correlated with ((11)C)PIB retention in the bilateral frontal and right anterior cingulate. ((11)C)PIB retention was greater in the bilateral frontal cortex of patients with AD with apathy than those of without apathy. Overlapping areas between the two analyses were the bilateral orbitofrontal gyrus and left superior frontal gyrus. Other NPI subscales were not correlated with ((11)C)PIB retention. Voxel-based morphometry analysis of MRI showed no significant cluster of correlation between grey matter volume and NPI subscales. CONCLUSIONS: This study revealed that prefrontal Aß deposition correlates with apathy.

Imaging of amyloid deposition in human brain using positron emission tomography and [18F]FACT: comparison with [11C]PIB.

PURPOSE: The characteristic neuropathological changes in Alzheimer's disease (AD) are deposition of amyloid senile plaques and neurofibrillary tangles. The (18)F-labeled amyloid tracer, [(18)F]2-[(2-{(E)-2-[2-(dimethylamino)-1,3-thiazol-5-yl]vinyl}-1,3-benzoxazol-6-yl)oxy]-3-fluoropropan-1-ol (FACT), one of the benzoxazole derivatives, was recently developed. In the present study, deposition of amyloid senile plaques was measured by positron emission tomography (PET) with both [(11)C]Pittsburgh compound B (PIB) and [(18)F]FACT in the same subjects, and the regional uptakes of both radiotracers were directly compared. METHODS: Two PET scans, one of each with [(11)C]PIB and [(18)F]FACT, were performed sequentially on six normal control subjects, two mild cognitive impairment (MCI) patients, and six AD patients. The standardized uptake value ratio of brain regions to the cerebellum was calculated with partial volume correction using magnetic resonance (MR) images to remove the effects of white matter accumulation. RESULTS: No significant differences in the cerebral cortical uptake were observed between normal control subjects and AD patients in [(18)F]FACT studies without partial volume correction, while significant differences were observed in [(11)C]PIB. After partial volume correction, the cerebral cortical uptake was significantly larger in AD patients than in normal control subjects for [(18)F]FACT studies as well as [(11)C]PIB. Relatively lower uptakes of [(11)C]PIB in distribution were observed in the medial side of the temporal cortex and in the occipital cortex as compared with [(18)F]FACT. Relatively higher uptake of [(11)C]PIB in distribution was observed in the frontal and parietal cortices. CONCLUSION: Since [(18)F]FACT might bind more preferentially to dense-cored amyloid deposition, regional differences in cerebral cortical uptake between [(11)C]PIB and [(18)F]FACT might be due to differences in regional distribution between diffuse and dense-cored amyloid plaque shown in the autoradiographic and histochemical assays of postmortem AD brain sections.

Synthesis and biochemical characterization of naphthoquinone derivatives targeting bacterial histidine kinases.

Waldiomycin is an inhibitor of histidine kinases (HKs). Although most HK inhibitors target the ATP-binding region, waldiomycin binds to the intracellular dimerization domain (DHp domain) with its naphthoquinone moiety presumed to interact with the conserved H-box region. To further develop inhibitors targeting the H-box, various 2-aminonaphthoquinones with cyclic, aliphatic, or aromatic amino groups and naphtho [2,3-d] isoxazole-4,9-diones were synthesized. These compounds were tested for their inhibitory activity (IC50) against WalK, an essential HK for Bacillus subtilis growth, and their minimum inhibitory concentrations (MIC) against B. subtilis. As a result, 11 novel HK inhibitors were obtained as naphthoquinone derivatives (IC50: 12.6-305 µM, MIC: 0.5-128 µg ml-1). The effect of representative compounds on the expression of WalK/WalR regulated genes in B. subtilis was investigated. Four naphthoquinone derivatives induced the expression of iseA (formerly yoeB), whose expression is negatively regulated by the WalK/WalR system. This suggests that these compounds inhibit WalK in B. subtilis cells, resulting in antibacterial activity. Affinity selection/mass spectrometry analysis was performed to identify whether these naphthoquinone derivatives interact with WalK in a manner similar to waldiomycin. Three compounds were found to competitively inhibit the binding of waldiomycin to WalK, suggesting that they bind to the H-box region conserved in HKs and inhibit HK activity.

The connector SafA interacts with the multi-sensing domain of PhoQ in Escherichia coli.

Sensor histidine kinases of two-component signal transduction systems (TCSs) respond to various environmental signals and transduce the external stimuli across the cell membrane to their cognate response regulators. Recently, membrane proteins that modulate sensory systems have been discovered. Among such proteins is SafA, which activates the PhoQ/PhoP TCS by direct interaction with the sensor PhoQ. SafA is directly induced by the EvgS/EvgA TCS, thus connecting the two TCSs, EvgS/EvgA and PhoQ/PhoP. We investigated how SafA interacted with PhoQ. Bacterial two-hybrid and reporter assays revealed that the C-terminal region (41-65 aa) of SafA activated PhoQ at the periplasm. Adding synthetic SafA(41-65) peptide to the cell culture also activated PhoQ/PhoP. Furthermore, direct interaction between SafA(41-65) and the sensor domain of PhoQ was observed by means of surface plasmon resonance. NMR spectroscopy of (15) N-labelled PhoQ sensor domain confirmed that SafA and Mg(2+) provoked a different conformational change of PhoQ. Site-directed mutagenesis studies revealed that R53, within SafA(41-65), was important for the activation of PhoQ, and D179 of the PhoQ sensor domain was required for its activation by SafA. SafA activated PhoQ by a different mechanism from cationic antimicrobial peptides and acidic pH, and independent of divalent cations and MgrB.

Mechanism of activation of PhoQ/PhoP two-component signal transduction by SafA, an auxiliary protein of PhoQ histidine kinase in Escherichia coli.

The PhoQ/PhoP two-component signal transduction system in Escherichia coli is activated by SafA, a small membrane protein that modifies the PhoQ histidine kinase. The SafA C-terminal domain (41-65 aa) interacts directly with the sensory domain of PhoQ at the periplasm. We used in vitro and in vivo strategies to elucidate the way SafA modifies the PhoQ/PhoP phosphorelay system. First, the enzymatic activities of membranes from cells overexpressing PhoQ and cells expressing both PhoQ and SafA were compared in vitro. Increased autophosphorylation of PhoQ was observed in the presence of SafA, but it did not increase the dephosphorylation of phospho-PhoP by PhoQ. In addition, SafA increased the phospho-PhoP level on the phosphotransfer assay. We confirmed that induction of SafA results in an accumulation of phospho-PhoP in vivo by the Phos-tag system. Our results suggest that the accumulation of phospho-PhoP is linked to activation of PhoQ autophosphorylation by SafA.

Isolation and characterization of signermycin B, an antibiotic that targets the dimerization domain of histidine kinase WalK.

The WalK (histidine kinase)/WalR (response regulator) two-component signal transduction system is a master regulatory system for cell wall metabolism and growth. This system is conserved in low G+C Gram-positive bacteria, including Bacillus subtilis, Staphylococcus aureus, Enterococcus faecalis, and Streptococcus mutans. In this study, we found the first antibiotic that functions as a WalK inhibitor (signermycin B) by screening 10,000 Streptomyces extracts. The chemical structure (C(23)H(35)NO(4); molecular weight, 389.5) comprises a tetramic acid moiety and a decalin ring. Signermycin B exhibited antimicrobial activity, with MIC values ranging from 3.13 µg/ml (8 µM) to 6.25 µg/ml (16 µM) against Gram-positive bacteria that possess the WalK/WalR two-component signal transduction system, including the drug-resistant bacteria methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. The half-maximal inhibitory concentrations of signermycin B against WalK in these organisms ranged from 37 to 61 µM. To determine the mechanism of action of signermycin B, surface plasmon resonance response analysis with the two WalK domains of Bacillus subtilis and competition assay with ATP were performed. The results showed that signermycin B binds to the dimerization domain but not the ATP-binding domain of WalK. In the presence of the cross-linker glutaraldehyde, signermycin B did not cause protein aggregation but interfered with the cross-linking of WalK dimers. These results suggest that signermycin B targets the conserved dimerization domain of WalK to inhibit autophosphorylation. In Bacillus subtilis and Staphylococcus aureus, signermycin B preferentially controlled the WalR regulon, thereby inhibiting cell division. These phenotypes are consistent with those of cells starved for the WalK/WalR system.

Roles of Two-Component Signal Transduction Systems in Shigella Virulence.

Two-component signal transduction systems (TCSs) are widespread types of protein machinery, typically consisting of a histidine kinase membrane sensor and a cytoplasmic transcriptional regulator that can sense and respond to environmental signals. TCSs are responsible for modulating genes involved in a multitude of bacterial functions, including cell division, motility, differentiation, biofilm formation, antibiotic resistance, and virulence. Pathogenic bacteria exploit the capabilities of TCSs to reprogram gene expression according to the different niches they encounter during host infection. This review focuses on the role of TCSs in regulating the virulence phenotype of Shigella, an intracellular pathogen responsible for severe human enteric syndrome. The pathogenicity of Shigella is the result of the complex action of a wide number of virulence determinants located on the chromosome and on a large virulence plasmid. In particular, we will discuss how five TCSs, EnvZ/OmpR, CpxA/CpxR, ArcB/ArcA, PhoQ/PhoP, and EvgS/EvgA, contribute to linking environmental stimuli to the expression of genes related to virulence and fitness within the host. Considering the relevance of TCSs in the expression of virulence in pathogenic bacteria, the identification of drugs that inhibit TCS function may represent a promising approach to combat bacterial infections.