Dual Redox Regulation of the DNA-Binding Activity of the Response Regulator RpaB in the Cyanobacterium Synechocystis sp. PCC 6803.

The response regulator RpaB plays a central role in transcriptional regulation of photosynthesis-related genes in cyanobacteria. RpaB is phosphorylated by its cognate histidine kinase Hik33 and functions as both an activator and a repressor under low-light conditions, whereas its phosphorylation level and DNA-binding activity promptly decrease upon the upshift of photon flux density, causing changes in the gene expression profile. In this study, we assessed the possibility of redox regulation of the DNA-binding activity of RpaB in Synechocystis sp. PCC 6803 by the addition of inhibitors of photosynthetic electron transport, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, or the reducing agent dithiothreitol under different photon flux densities. Analysis of the phosphorylation level of RpaB revealed that reduction of QA and increase in the availability of reducing equivalents at the acceptor side of photosystem I (PSI) can independently trigger dephosphorylation. The redox-state-dependent regulation by an unidentified thiol other than Cys59 of RpaB is prerequisite for the phosphorylation-dependent regulation of the DNA-binding activity. Environmental signals, recognized by Hik33, and metabolic signals recognized as the availability of reducing equivalents, must be integrated at the master regulator RpaB, in order to attain the flexible regulation of acclimatory responses.

Zonisamide effects on sleep problems and depressive symptoms in Parkinson's disease.

BACKGROUND: We aimed to evaluate the effect of zonisamide (ZNS) on motor symptoms and nonmotor symptoms such as depressive symptoms and sleep problems in Parkinson's disease (PD) patients with or without tremor. METHODS: We conducted a 3-month, open-label study to assess the effects of ZNS on motor symptoms, depressive symptoms and sleep problems. Twenty levodopa-treated PD patients with motor fluctuation completed the study. Patients received 25-50 mg/day of ZNS and were assessed for the Japanese version of the Movement Disorder Society Revision of the Unified PD Rating Scale (MDS-UPDRS) parts I, III, and IV, PD Sleep Scale (PDSS)-2, Beck depression inventory-2 (BDI-II), and PD Questionnaire (PDQ-8) at baseline and after 1, 2 and 3 months of treatment. Patients were categorized into the tremor group and nontremor group to assess changes in clinical parameters. RESULTS: At 3 months, the scores on the MDS-UPDRS parts I, III and IV significantly improved and off-time reduced compared to baseline. Additionally, the PDSS-2 total score significantly decreased at 3 months. Although there were no significant differences in changes in UPDRS part I, III, or IV between the groups after ZNS treatment, the tremor group had significant improvements in PDSS-2 at 3 months and BDI-II at 1, 2 and 3 months compared with the nontremor group. CONCLUSION: We showed the beneficial effects of ZNS on motor symptoms and sleep problems in levodopa-treated PD patients with motor fluctuation. ZNS may be more effective for several nonmotor symptoms in PD patients with tremor compared with those without tremor.

Iron accumulation in the choroid plexus, ependymal cells and CNS parenchyma in a rat strain with low-grade haemolysis of fragile macrocytic red blood cells.

Iron accumulation in the CNS is associated with many neurological diseases via amplification of inflammation and neurodegeneration. However, experimental studies on iron overload are challenging, since rodents hardly accumulate brain iron in contrast to humans. Here, we studied LEWzizi rats, which present with elevated CNS iron loads, aiming to characterise choroid plexus, ependymal, CSF and CNS parenchymal iron loads in conjunction with altered blood iron parameters and, thus, signifying non-classical entry sites for iron into the CNS. Non-haem iron in formalin-fixed paraffin-embedded tissue was detected via DAB-enhanced Turnbull Blue stainings. CSF iron levels were determined via atomic absorption spectroscopy. Ferroportin and aquaporin-1 expression was visualised using immunohistochemistry. The analysis of red blood cell indices and serum/plasma parameters was based on automated measurements; the fragility of red blood cells was manually determined by the osmotic challenge. Compared with wild-type animals, LEWzizi rats showed strongly increased iron accumulation in choroid plexus epithelial cells as well as in ependymal cells of the ventricle lining. Concurrently, red blood cell macrocytosis, low-grade haemolysis and significant haemoglobin liberation from red blood cells were apparent in the peripheral blood of LEWzizi rats. Interestingly, elevated iron accumulation was also evident in kidney proximal tubules, which share similarities with the blood-CSF barrier. Our data underscore the importance of iron gateways into the CNS other than the classical route across microvessels in the CNS parenchyma. Our findings of pronounced choroid plexus iron overload in conjunction with peripheral iron overload and increased RBC fragility in LEWzizi rats may be seminal for future studies of human diseases, in which similar constellations are found.

Bickerstaff's Brainstem Encephalitis Suspected as Functional Neurologic Disorders.

Functional neurologic disorders feature nervous system symptoms that cannot be explained by a neurological disease or other medical condition. The patient described here was a 21-year-old Japanese woman who was initially diagnosed with a functional neurologic disorder based on numbness and weakness of the limbs with no abnormalities in routine examinations. Further detailed examinations revealed monocytes in cerebrospinal fluid (CSF), and electroencephalography revealed widespread, low-voltage, slow waves with concentrated spindle waves. Thus, encephalitis was suspected, and steroid pulse therapy was initiated. Her symptoms subsequently improved. Afterward, CSF analysis was positive for serum anti-GQ1b IgG antibodies. We made a final diagnosis of Bickerstaff's brainstem encephalitis (BBE). Our report describes the difficult differentiation of functional neurologic disorders from BBE. Physicians and psychiatrists should be aware of BBE.

Gene regulatory network and its constituent transcription factors that control nitrogen-deficiency responses in rice.

Increase in the nitrogen (N)-use efficiency and optimization of N response in crop species are urgently needed. Although transcription factor-based genetic engineering is a promising approach for achieving these goals, transcription factors that play key roles in the response to N deficiency have not been studied extensively. Here, we performed RNA-seq analysis of root samples of 20 Asian rice (Oryza sativa) accessions with differential nutrient uptake. Data obtained from plants exposed to N-replete and N-deficient conditions were subjected to coexpression analysis and machine learning-based pathway inference to dissect the gene regulatory network required for the response to N deficiency. Four transcription factors, including members of the G2-like and bZIP families, were predicted to function as key regulators of gene transcription within the network in response to N deficiency. Cotransfection assays validated inferred novel regulatory pathways, and further analyses using genome-edited knockout lines suggested that these transcription factors are important for N-deficiency responses in planta. Many of the N deficiency-responsive genes, including those encoding key regulators within the network, were coordinately regulated by transcription factors belonging to different families. Transcription factors identified in this study could be valuable for the modification of N response and metabolism.

Determinants of Low Body Mass Index in Patients with Parkinson's Disease: A Multicenter Case-Control Study.

BACKGROUND: In Parkinson's disease (PD) patients, the factors related to weight loss remain unclear. OBJECTIVE: To investigate determinants of low body mass index (BMI) in PD patients. METHODS: We identified factors associated with low BMI in PD patients in a multicenter case-control study. A total of 435 PD patients and 401 controls were included. RESULTS: The mean BMI was significantly lower in PD patients than in controls (22.0±3.4 kg/m2 vs. 25.4±4.3 kg/m2), with an adjusted odds ratio (AOR) of 3.072 (95% CI, 2.103-4.488; p < 0.001) for low BMI (<22 kg/m2) in PD. Compared to the high-BMI PD group (>22 kg/m2), the low-BMI PD group (<22 kg/m2) had more women; a longer disease duration; higher revised Movement Disorder Society Unified PD Rating Scale (MDS-UPDRS) II and IV scores; an increased levodopa equivalent dose (LED); and increased constipation, visual hallucination, dysphagia, dyskinesia and wearing off rates. There were no between-group differences in depression, anhedonia, apathy, sleep problems and daytime sleepiness. Multivariable analysis showed that visual hallucination (AOR, 2.408; 95% CI, 1.074-5.399; p = 0.033) and the MDS-UPDRS IV (AOR, 1.155; 95% CI, 1.058-1.260; p = 0.001) contributed to low BMI after controlling for clinical factors. In a second model, visual hallucination (AOR, 2.481; 95% CI, 1.104-5.576; p = 0.028) and dyskinesia (sum of the MDS-UPDRS 4.3-4.6) (AOR, 1.319; 95% CI, 1.043-1.668; p = 0.021) significantly contributed to low BMI. CONCLUSION: PD patients were 3 times more likely than healthy controls to have a low BMI. Motor complications, particularly dyskinesia, and visual hallucination were significantly associated with low BMI in PD patients.

Minocycline Alleviates Cluster Formation of Activated Microglia and Age-dependent Dopaminergic Cell Death in the Substantia Nigra of Zitter Mutant Rat.

Microglial activation is a component of neurodegenerative pathology. Here, we examine whether activated microglia participate in age-related dopaminergic (DA) cell death in the substantia nigra pars compacta (SNc) of the zitter (zi/zi) rat, a mutant characterized by deletion of the attractin gene. Confocal microscopy with double-immunohistochemical staining revealed activated microglia-formed cell-clusters surrounding DA neurons in the SNc from 2 weeks after birth. An immunoelectron microscopic study showed that the cytoplasm of activated microglia usually contains phagosome-like vacuoles and lamellar inclusions. Expression levels of the pro-inflammatory cytokines interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) were increased in the midbrain of 2-month-old zi/zi rats. Chronic treatment with the anti-inflammatory agent minocycline altered the morphology of the microglia, reduced cluster formation by the microglia, and attenuated DA cell death in the SNc, and reduced the expression of IL-1ß in the midbrain. These results indicate that activated microglia, at least in part and especially at the initial phase, contribute to DA cell death in the SNc of the zi/zi rat.

Leg restlessness preceding the onset of motor symptoms of Parkinson disease: A case series of 5 patients.

Patients with Parkinson disease (PD) often show restless legs syndrome (RLS), leg motor restlessness (LMR) and other leg restlessness (OLR) related to sensorimotor symptoms.Here, we describe 5 patients who presented with leg restlessness as an early manifestation of PD.In case 1, the patient had leg restlessness that was not LMR or RLS and preceded the onset of motor symptoms by 1 year. In case 2, LMR preceded motor symptoms by 2 years. Case 3 had unilateral RLS symptoms on the left side of the body for 33 years. Two and a half years after the spread of RLS symptoms to the right leg with increased frequency of left-sided RLS symptoms, the patient developed PD at the age of 58 years. In cases 4 and 5, RLS symptoms preceded motor symptoms by 3 months and 1 month, respectively. All patients developed Parkinsonism within 3 years (median, 1.0 year; range 0.083-2.5 years) after initial onset or exacerbation of leg restlessness. All patients had frequent leg restlessness symptoms (6-7 days per week). In our series, the preceding leg restlessness was unilateral and confined to the dominant side of the subsequent Parkinsonism, or preceding leg restlessness was bilateral but dominant on the dominant side of the subsequent Parkinsonism.Clinicians should be aware that late-onset leg restlessness (>50 years of age) including RLS, LMR, and OLR, particularly if frequent and asymmetrical, can be an early nonmotor manifestation of PD.

Biocomputational Analyses and Experimental Validation Identify the Regulon Controlled by the Redox-Responsive Transcription Factor RpaB.

Oxygenic photosynthesis requires the coordination of environmental stimuli with the regulation of transcription. The transcription factor RpaB is conserved from the simplest unicellular cyanobacteria to complex eukaryotic algae, representing more than 1 billion years of evolution. To predict the RpaB-controlled regulon in the cyanobacterium Synechocystis, we analyzed the positional distribution of binding sites together with high-resolution mapping data of transcriptional start sites (TSSs). We describe more than 150 target promoters whose activity responds to fluctuating light conditions. Binding sites close to the TSS mediate repression, whereas sites centered ∼50 nt upstream mediate activation. Using complementary experimental approaches, we found that RpaB controls genes involved in photoprotection, cyclic electron flow and state transitions, photorespiration, and nirA and isiA for which we suggest cross-regulation with the transcription factors NtcA or FurA. The deep integration of RpaB with diverse photosynthetic gene functions makes it one of the most important and versatile transcriptional regulators.

Microglia pre-activation and neurodegeneration precipitate neuroinflammation without exacerbating tissue injury in experimental autoimmune encephalomyelitis.

Human inflammatory or neurodegenerative diseases, such as progressive multiple sclerosis (MS), occur on a background of age-related microglia activation and iron accumulation as well as pre-existing neurodegeneration. Most experimental models for CNS diseases, however, are induced in rodents, which are naturally characterized by a homeostatic microglia phenotype, low cellular iron load and absence of neurodegeneration. Here, we show that naïve LEWzizi rats - Lewis rats with a zitter rat background - show a spontaneous phenotype partly mimicking the changes seen in human aging and particularly in the normal-appearing white and grey matter of patients with progressive MS. Using this model system, we further aimed to investigate (i) whether the acute monophasic MS model experimental autoimmune encephalomyelitis (EAE) transforms into chronic progressive disease and (ii) whether EAE-induced neuroinflammation and tissue damage aggravate on the LEWzizi background. We found that the pre-existing LEWzizi-specific pathology precipitated EAE-related neuroinflammation into forebrain areas, which are devoid of EAE lesions in normal Lewis rats. However, EAE-related tissue damage was neither modified by the LEWzizi-specific pathology nor did EAE-induced neuroinflammation modify the LEWzizi-related pathological process. Our data indicate that the interaction between pre-activated microglia and CD4+ autoreactive T cells during the induction and propagation of tissue damage in the CNS is limited.

Interaction of the GntR-family transcription factor Sll1961 with thioredoxin in the cyanobacterium Synechocystis sp. PCC 6803.

Changes in the redox state of the photosynthetic electron transport chain act as a signal to trigger acclimation responses to environmental cues and thioredoxin has been suggested to work as a key factor connecting the redox change with transcriptional regulation in the cyanobacterium Synechocystis sp. PCC 6803. We screened for redox-dependent transcription factors interacting with thioredoxin M (TrxM) and isolated the GntR-type transcription factor Sll1961 previously reported to be involved in acclimation responses of the photosynthetic machinery. Biochemical analyses using recombinant Sll1961 proteins of wild type and mutants of three cysteine residues, C124, C229 and C307, revealed that an intramolecular disulfide bond is formed between C229 and C307 under oxidizing conditions and TrxM can reduce it by attacking C307. Sll1961 exists in a dimeric form of about 80 kDa both under reducing and oxidizing conditions. C124 can form an intermolecular disulfide bond but it is not essential for dimerization. Based on these observations, tertiary structure models of the Sll1961 homodimer and the Sll1961-TrxM complex were constructed.

A Card-type Odor Identification Test for Japanese Patients with Parkinson's Disease and Related Disorders.

Objective The characteristics of olfactory impairment in Parkinson's disease (PD), multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) have not been determined in detail. We assessed the olfactory function among PD, MSA and PSP patients. Methods A card-type odor identification test, Open Essence (OE, Wako, Japan), which consists of 12 different odorants familiar to Japanese subjects, was administered to 98 PD patients, 32 MSA patients, 17 PSP patients and 96 control subjects ≥50 years of age. Results The PD patients had significantly lower OE scores than the other groups. The OE scores of the MSA and PSP patients fell between those of the PD patients and the control subjects. A cut-off OE score of 6 was beneficial for differentiating PD patients from controls with 84.7% sensitivity and 85.4% specificity. A cut-off OE score of 4 had 60.2% sensitivity and 77.6% specificity for differentiating PD patients from MSA and PSP patients. The correct answer rates for the curry, Japanese orange and perfume odorants in the PD patients were lower than those in the MSA and PSP patients and controls. The PD patients also had the highest ratio of "not detected" choices across the 12 odors. Conclusion Marked olfactory impairment was a feature of the patients with PD, while mild olfactory impairment was observed in those with MSA or PSP. The answer patterns and the specific odorants may also be useful in differentiating PD from related disorders.

Istradefylline improves daytime sleepiness in patients with Parkinson's disease: An open-label, 3-month study.

BACKGROUND: Istradefylline, a selective adenosine A2A receptor antagonist, has been reported to improve daily "off time" and motor symptoms in patients with Parkinson's disease (PD). However, the effect of istradefylline on sleep problems has not been thoroughly investigated. METHODS: We evaluated the effect of istradefylline on daytime sleepiness, sleep disturbances, and motor symptoms in 22 PD patients who were affected by the wearing off phenomenon in an open-label, 3-month study. Participants received 20-40mg/day istradefylline once daily (morning) over a 3-month period. The Epworth Sleepiness Scale (ESS), PD sleep scale (PDSS)-2 and PD Questionnaire (PDQ-8) were administered at baseline, 2weeks, 1month, 2months and 3months. At baseline and 3months, patients were evaluated on the Movement Disorder Society Revision of the Unified PD Rating Scale (MDS-UPDRS) parts III and IV. RESULTS: Twenty-one patients (95.5%) completed the study. At 3months, MDS-UPDRS part III (-5.3, p=0.0002) and part IV (-2.5, p=0.001) scores improved and off time decreased significantly (-50.1min, p=0.0004). PDQ-8 scores were unchanged at 3months. ESS scores decreased significantly at 2months and 3months (-2.4 and -3.3, respectively, p<0.0001), but the total PDSS-2 scores did not change. CONCLUSION: Istradefylline improved daytime sleepiness in PD patients, possibly through its effect on enhancing alertness. In addition, the lack of significant changes in the total PDSS-2 scores over the study period suggests istradefylline had no negative impact on sleep.

Impact of sleep-related symptoms on clinical motor subtypes and disability in Parkinson's disease: a multicentre cross-sectional study.

OBJECTIVES: To investigate the impact of sleep disturbances on Parkinson's disease (PD) clinical motor subtypes and disease-related disability in a multicentre setting. METHODS: We report a cross-sectional relationship between sleep-related symptoms and clinical motor subtypes (tremor dominant (TD); intermediate; postural instability and gait disturbances (PIGDs)) identified in a multicentre study, including 436 patients with PD and 401 age-matched controls. PD-related sleep problems (PD-SP), excessive daytime sleepiness (EDS) and probable REM sleep behaviour disorder (pRBD) were evaluated using the PD sleep scale (PDSS)-2, Epworth Sleepiness Scale (ESS) and RBD screening questionnaire-Japanese version (RBDSQ-J), respectively. RESULTS: PD-SP (PDSS-2 ≥18; 35.1% vs 7.0%), EDS (ESS ≥10; 37.8% vs 15.5%) and pRBD (RBDSQ-J ≥5; 35.1% vs 7.7%) were more common in patients with PD than in controls. The prevalence of restless legs syndrome did not differ between patients with PD and controls (3.4% vs 2.7%). After adjusting for age, sex, disease duration and Movement Disorder Society-Unified PD Rating Scale (MDS-UPDRS) part III score, the PIGD group had higher PDSS-2 and ESS scores than the TD group. The RBDSQ-J scores did not differ among the TD, intermediate and PIGD groups. A stepwise regression model predicting the MDS-UPDRS part II score identified the Hoehn and Yahr stage, followed by the number of sleep-related symptoms (PD-SP, EDS and pRBD), disease duration, MDS-UPDRS part III score, PIGD subtype, depression and MDS-UPDRS part IV score as significant predictors. CONCLUSION: Our study found a significant relationship between sleep disturbances and clinical motor subtypes. An increased number of sleep-related symptoms had an impact on disease-related disability.

Acclimation of Oxygenic Photosynthesis to Iron Starvation Is Controlled by the sRNA IsaR1.

Oxygenic photosynthesis crucially depends on proteins that possess Fe2+ or Fe/S complexes as co-factors or prosthetic groups. Here, we show that the small regulatory RNA (sRNA) IsaR1 (Iron-Stress-Activated RNA 1) plays a pivotal role in acclimation to low-iron conditions. The IsaR1 regulon consists of more than 15 direct targets, including Fe2+-containing proteins involved in photosynthetic electron transfer, detoxification of anion radicals, citrate cycle, and tetrapyrrole biogenesis. IsaR1 is essential for maintaining physiological levels of Fe/S cluster biogenesis proteins during iron deprivation. Consequently, IsaR1 affects the acclimation of the photosynthetic apparatus to iron starvation at three levels: (1) directly, via posttranscriptional repression of gene expression; (2) indirectly, via suppression of pigment; and (3) Fe/S cluster biosynthesis. Homologs of IsaR1 are widely conserved throughout the cyanobacterial phylum. We conclude that IsaR1 is a critically important riboregulator. These findings provide a new perspective for understanding the regulation of iron homeostasis in photosynthetic organisms.

Anhedonia and its correlation with clinical aspects in Parkinson's disease.

Anhedonia is one of the non-motor symptoms observed in the Parkinson's disease (PD). However, there is no clear relationship between anhedonia and its correlation with other symptoms of PD. The aim of this study is to evaluate the characteristics of anhedonia and its correlation with clinical aspects of PD in a relatively large cohort. We enrolled 318 patients with PD and 62 control subjects for this study. Patients and subjects were tested using the Snaith-Hamilton Pleasure Scale Japanese version and the Beck Depression Inventory 2nd edition for the assessment of anhedonia and depression. We also investigated the correlation among clinical aspects of PD, anhedonia, and depression in patients with PD. The Snaith-Hamilton Pleasure Scale Japanese version and the Beck Depression Inventory 2nd edition scores were significantly higher in patients with PD than in control subjects (p=0.03 and p=0.0006, respectively). All PD patients with anhedonia had a significantly higher score on the unified Parkinson's disease rating scale (UPDRS) parts I and II compared to PD patients without anhedonia. Additionally, all PD patients with depression scored significantly higher on UPDRS part I-IV than PD patients without depression. The patients with anhedonia and without depression had mild motor severity and their treatment was relatively low dosage. These results suggest that anhedonia and depression are slightly linked, but not the same. PD patients with only anhedonia may be closely linked apathy found in untreated early stages of PD.

A Japanese multicenter survey characterizing pain in Parkinson's disease.

BACKGROUND: Pain is a frequent, troublesome symptom of PD but is under-recognized and poorly understood. AIM: We characterized pain prevalence, severity, and location in PD, to better understand its pathophysiology and improve diagnosis and treatment. SUBJECTS AND METHODS: A cross-sectional controlled study was conducted at 19 centers across Japan. A total of 632 subjects with Mini-Mental State Examination scores ≥24 were enrolled, including 324 PD patients and 308 controls. Sex and mean age did not differ between the two groups. Demographic and clinical data were collected. Pain was assessed using questionnaires, the SF-36v2 bodily pain scale, and a body illustration for patients to indicate the location of pain in 45 anatomical areas. RESULTS: Pain prevalence in the PD group was 78.6%, significantly higher than in controls (49.0%), as was its severity. There was no correlation between SF-36v2 score and motor scores, such as Unified Parkinson's Disease Rating Scale III or Hoehn & Yahr scores. Pain distribution was similar between groups, predominantly in the lower back, followed by the gluteal region, lower legs, thighs, posterior neck, and shoulders. CONCLUSION: Pain is a significant problem in the Japanese PD population and we discuss its pathophysiology.

A Feed-Forward Loop Consisting of the Response Regulator RpaB and the Small RNA PsrR1 Controls Light Acclimation of Photosystem I Gene Expression in the Cyanobacterium Synechocystis sp. PCC 6803.

Since cyanobacteria need to decrease PSI content to avoid absorption of excess light energy, down-regulation of PSI gene expression is one of the key characteristics of the high-light (HL) acclimation response. The transcriptional regulator RpaB and the small RNA PsrR1 (photosynthesis regulatory RNA1) have been suggested to be the two most critical factors for this response in Synechocystis sp. PCC 6803. In this study, we found that the HLR1 DNA-binding motif, the recognition sequence for RpaB, is highly conserved in the core promoter region of the psrR1 gene among cyanobacterial species. Gel mobility shift assay revealed that RpaB binds to the HLR1 sequence of psrR1 in vitro. RNA gel blot analysis together with chromatin affinity purification (ChAP) analysis suggested that PSI genes are activated and the psrR1 gene is repressed by the binding of RpaB under low-light (LL) conditions. A decrease in DNA binding affinity of RpaB occurs within 5 min after the shift from LL to HL conditions, leading to the prompt decrease in PSI promoter activity together with derepression of psrR1 gene expression. Accumulating PsrR1 molecules then prevent translation from pre-existing PSI transcripts. By this dual repression at transcriptional and post-transcriptional levels, rapid and strict down-regulation of PSI expression under HL is secured. Our findings suggest that RpaB and PsrR1 constitute a feed-forward loop for the regulation of PSI gene expression to achieve a rapid acclimation response to the damaging HL conditions.

Correction: identification of OmpR-family response regulators interacting with thioredoxin in the cyanobacterium Synechocystis sp. PCC 6803.

[This corrects the article DOI: 10.1371/journal.pone.0119107.].

Identification of OmpR-family response regulators interacting with thioredoxin in the Cyanobacterium Synechocystis sp. PCC 6803.

The redox state of the photosynthetic electron transport chain is known to act as a signal to regulate the transcription of key genes involved in the acclimation responses to environmental changes. We hypothesized that the protein thioredoxin (Trx) acts as a mediator connecting the redox state of the photosynthetic electron transport chain and transcriptional regulation, and established a screening system to identify transcription factors (TFs) that interact with Trx. His-tagged TFs and S-tagged mutated form of Trx, TrxMC35S, whose active site cysteine 35 was substituted with serine to trap the target interacting protein, were co-expressed in E. coli cells and Trx-TF complexes were detected by immuno-blotting analysis. We examined the interaction between Trx and ten OmpR family TFs encoded in the chromosome of the cyanobacterium Synechocystis sp. PCC 6803 (S.6803). Although there is a highly conserved cysteine residue in the receiver domain of all OmpR family TFs, only three, RpaA (Slr0115), RpaB (Slr0947) and ManR (Slr1837), were identified as putative Trx targets [corrected].The recombinant forms of wild-type TrxM, RpaA, RpaB and ManR proteins from S.6803 were purified following over-expression in E. coli and their interaction was further assessed by monitoring changes in the number of cysteine residues with free thiol groups. An increase in the number of free thiols was observed after incubation of the oxidized TFs with Trx, indicating the reduction of cysteine residues as a consequence of interaction with Trx. Our results suggest, for the first time, the possible regulation of OmpR family TFs through the supply of reducing equivalents from Trx, as well as through the phospho-transfer from its cognate sensor histidine kinase.