Non-invasive administration of AAV to target lung parenchymal cells and develop SARS-CoV-2-susceptible mice.

Adeno-associated virus (AAV)-mediated gene delivery holds great promise for gene therapy. However, the non-invasive delivery of AAV for lung tissues has not been adequately established. Here, we revealed that the intratracheal administration of an appropriate amount of AAV2/8 predominantly targets lung tissue. AAV-mediated gene delivery that we used in this study induced the expression of the desired protein in lung parenchymal cells, including alveolar type II cells. We harnessed the technique to develop severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-susceptible mice. Three kinds of immune function-relevant gene knockout (KO) mice were transduced with AAV encoding human angiotensin-converting enzyme 2 (hACE2) and then injected with SARS-CoV-2. Among these mice, type I interferon receptor (IFNAR) KO mice showed increased viral titer in the lungs compared to that in the other KO mice. Moreover, nucleocapsid protein of SARS-CoV-2 and multiple lesions in the trachea and lung were observed in AAV-hACE2-transduced, SARS-CoV-2-infected IFNAR KO mice, indicating the involvement of type I interferon signaling in the protection of SARS-CoV-2. In this study, we demonstrate the ease and rapidness of the intratracheal administration of AAV for targeting lung tissue in mice, and this can be used to study diverse pulmonary diseases.

Evaluation of 28-day repeated oral dose toxicity of aluminum chloride in rats.

The present study investigated the potential adverse effects of aluminum chloride (AlCl3) following a 4-week repeated oral administration in Sprague-Dawley rats. The test article was administered once daily by gavage to male and female rats at dose levels of 0, 100, 300, and 900 mg/kg/day for 4 weeks. After administration of AlCl3 at 900 mg/kg/day, treatment-related systemic toxicity manifested as significant increases in salivation incidence, neutrophil percentage, reticulocytes, serum triglyceride, adrenal gland and liver weights, and single-hepatocyte necrosis, as well as significant decreases in body weight gain, food intake, hemoglobin, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration (MCHC), lymphocyte percentage, serum total protein and albumin, and thymus weight in male rats; and significant increases in salivation incidence, serum triglyceride, and liver weight, as well as a significant decrease in lymphocyte percentage in female rats. At 300 mg/kg/day, a significant decrease in MCHC was found in male rats, but not in female rats. However, this finding was not toxicologically significant because the reduction was minimal and was not accompanied by changes in any other parameters. No treatment-related effects were observed in the 100 mg/kg/day group of both genders. Under the experimental conditions of this study, the target organs of AlCl3 were determined to be the blood, liver, and thymus in rats. The no-observed-adverse-effect level was found to be 300 mg/kg/day in rats of both genders.

Effect of Yijin-Tang, an Oriental Traditional Formula, on Allergic Responses Using an Ovalbumin-Induced Murine Asthma Model.

Yijin-tang is an oriental traditional herb used to treat inflammatory diseases. In the present study, we investigated the protective effects of Yijin-tang water extract (YTE) using an ovalbumin- (OVA-) induced asthma model, focusing on the antioxidant and anti-inflammatory properties of the herb. BALB/c mice were intraperitoneally injected with OVA on days 0 and 14 and then challenged with OVA on days 21, 22, and 23. The animals were orally administered YTE (200 and 400 mg/kg) from days 18 to 23, and this was found to significantly decrease airway hyperresponsiveness and release of inflammatory cells, cytokines, and OVA-specific immunoglobulin E in mice with asthma. In addition, YTE was associated with a marked reduction in airway inflammation and mucus production in lung tissue of mice with asthma. Furthermore, YTE suppressed the expression of matrix metalloproteinase-9 and phosphorylation of ERK in the lungs, which in turn led to a reduction in inducible nitric oxide synthases and an elevation in reduced glutathione and heme oxygenase-1. In conclusion, YTE effectively suppressed allergic responses in mice with asthma and the effect was closely related to antioxidant and anti-inflammatory properties of the herb. Our results indicate that YTE may be a potential agent for the treatment of allergic asthma.

Comparative Assessment and External Validation of Hepatic Steatosis Formulae in a Community-Based Setting.

Several hepatic steatosis formulae have been validated in various cohorts using ultrasonography. However, none of these studies has been validated in a community-based setting using the gold standard method. Thus, the aim of this study was to externally validate hepatic steatosis formulae in community-based settings using magnetic resonance imaging (MRI). A total of 1301 community-based health checkup subjects who underwent liver fat quantification with MRI were enrolled in this study. Diagnostic performance was assessed using the area under the receiver operating characteristic curve (AUROC). Non-alcoholic fatty liver disease (NAFLD) liver fat score showed the highest diagnostic performance with an AUROC of 0.72, followed by Framingham steatosis index (0.70), hepatic steatosis index (HSI, 0.69), ZJU index (0.69), and fatty liver index (FLI, 0.68). There were considerable gray zones in three fatty liver prediction models using two cutoffs (FLI, 28.9%; HSI, 48.9%; and ZJU index, 53.6%). The diagnostic performance of NAFLD liver fat score for detecting steatosis was comparable to that of ultrasonography. The diagnostic agreement was 72.7% between NAFLD liver fat score and 70.9% between ultrasound and MRI. In conclusion, the NAFLD liver fat score showed the best diagnostic performance for detecting hepatic steatosis. Its diagnostic performance was comparable to that of ultrasonography in a community-based setting.

Silibinin Attenuates Silica Dioxide Nanoparticles-Induced Inflammation by Suppressing TXNIP/MAPKs/AP-1 Signaling.

Silica dioxide nanoparticles (SiONPs) have been applied to several fields, such as drug delivery and gene therapy. However, SiONPs are a constituent of fine dust and can induce excessive inflammatory responses in the lungs via the airways. Silibinin, a major component of silymarin, has been known for its anti-oxidant and anti-inflammatory effects. In the present study, we explored the protective effects of silibinin against SiONPs-induced airway inflammation and explored its underlying mechanism of action, focusing on thioredoxin-interacting protein (TXNIP)/mitogen-activated protein kinases (MAPKs) in vitro and in vivo. In SiONPs-stimulated NCI-H292 airway epithelial cells, silibinin treatment effectively suppressed the elevation of the mRNA expression of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1ß, which was accompanied by the reduction in the expression of TXNIP, MAPKs, and activator protein-1 (AP-1). In SiONPs-treated mice, silibinin administration inhibited the increase in inflammatory cell counts and proinflammatory mediators, and it alleviated airway inflammation by SiONPs exposure. In addition, silibinin administration effectively suppressed the elevation of TXNIP/MAPKs/AP-1 signaling by SiONPs exposure. Taken together, silibinin effectively inhibited SiONPs-induced inflammatory responses, and this effect was closely related to the inhibition of TXNIP/MAPK/AP-1 signaling. These results suggested that silibinin might be useful for reducing pulmonary inflammation induced by SiONPs.

Silica dioxide nanoparticles aggravate airway inflammation in an asthmatic mouse model via NLRP3 inflammasome activation.

Silica dioxide nanoparticles (SiONPs) are mainly used in the rubber industry; however, they are a major air pollutant in Asia. Thus, extensive research on this issue is required. In this study, we investigated the effects of SiONPs on asthma aggravation and elucidated the underlying mechanism using ovalbumin (OVA)-induced asthmatic mice model and in NCI-H292 cells. Mice exposed to SiONPs showed markedly increased Penh values, inflammatory cell counts, and inflammatory cytokine levels compared to OVA-induced asthmatic mice. Exposure to SiONPs also induced additional airway inflammation and mucus secretion with increases in protein expression levels of thioredoxin-interacting protein (TXNIP), NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome, and interleukin (IL)-1ß compared to those in OVA-induced asthmatic mice. Treatment of SiONPs in NCI-H292 cells also significantly increased mRNA expression levels of inflammatory cytokines accompanied with elevation in the levels of TXNIP, NLRP3 inflammasome, and IL-1ß proteins in a concentration-dependent manner. Taken together, exposure to SiONPs aggravated asthma development, which is closely related to inflammasome activation. Our results provide useful information about the toxicological effects of SiONPs on asthma exacerbation and suggest the need to avoid SiONP exposure especially in individuals with respiratory diseases.

Scrophularia koraiensis Nakai Attenuates Allergic Airway Inflammation via Suppression of NF-κB and Enhancement of Nrf2/HO-1 Signaling.

Scrophularia koraiensis Nakai (Scrophulariaceae) is a medicinal herb that grows in Korea and which has been widely used to treat fever, edema, neuritis and laryngitis. Hence, we evaluated the anti-inflammatory and antioxidant effects of the ethanol extract (SKE) of S. koraiensis Nakai in an ovalbumin (OVA)-induced mouse model. We injected 20 µg of OVA with 2 mg of aluminum on day 0 and day 14 to induce allergic airway inflammation in six-week-old BALB/c mice, and mice were challenged with 1% OVA by nebulization for 1 h on days 21, 22, and 23. SKE was orally administered at 20 mg/kg and 40 mg/kg from day 18 to 23, and its effects were compared with those of montelukast treatment. SKE significantly reduced proinflammatory cytokines, inflammatory cell counts, immunoglobulin-E, and airway hyperresponsiveness during the OVA-induced allergic airway inflammation model; it also reduced airway inflammation and mucus production. In addition, SKE reduced the OVA-induced nuclear factor kappa B (NF-κB) phosphorylation in lung tissues while enhancing nuclear factor erythroid-derived 2-related factor (Nrf-2) and heme oxygenase-1 (HO-1) expression. In conclusion, SKE showed the protective effects on OVA-induced allergic airway inflammation via the suppression of NF-κB phosphorylation and the enhancement of the Nrf2/HO-1 signaling pathway. These results indicate that SKE is a potential therapeutic agent for allergic airway inflammation.

Scrophularia buergeriana attenuates allergic inflammation by reducing NF-κB activation.

BACKGROUND: Scrophularia buergeriana Miq. (Scrophulariaceae) (SB) has been used as an oriental medicine for the treatment of inflammatory diseases, such as neuritis and pharyngolaryngitis. PURPOSE: We explored the therapeutic effects of S. buergeriana ethanol extract (SBE) on airway inflammation in ovalbumin (OVA)-induced asthmatic mice and lipopolysaccharide (LPS)-stimulated RAW264.7 cells. METHODS: Mice were intraperitoneally injected with OVA on days 0 and 14 to elevate the immune response. On days 21 to 23, the mice were challenged with OVA solution and SBE (20 and 40 mg/kg) was administered daily by oral gavage from days 18 to 23. RAW264.7 cells were pretreated with SBE 1 h before LPS stimulation. RESULTS: SBE administration effectively suppressed inflammatory cell infiltration, the expression of interleukin (IL)-5, IL-13, and IL-17, immunoglobulin E, and airway hyperresponsiveness in an OVA-induced allergic asthma model. A reduction in histological alterations, including airway inflammation and mucus hypersecretion, was observed. These effects of SBE were accompanied by a decrease in matrix metalloproteinase-9 (MMP-9) expression and nuclear factor kappa B (NF-κB) phosphorylation. These responses were observed in LPS-stimulated RAW264.7 cells. SBE treatment reduced the mRNA expression of tumor necrosis factor (TNF)-α, IL-6, and MMP-9, and NF-κB phosphorylation, in LPS-stimulated RAW264.7 cells. CONCLUSION: Our results indicated that SBE effectively attenuated airway inflammation in an OVA-induced allergic asthma model. These properties of SBE were thought to be involved in the suppression of NF-κB phosphorylation, suggesting that the material has the potential to regulate the development of allergic asthma.

Cisplatin-induced ototoxicity involves interaction of PRMT3 and cannabinoid system.

This study investigated whether protein arginine methyltransferase (PRMT) and the cannabinoid system are involved in cisplatin-induced ototoxicity. Cisplatin increased cytosine-cytosine-adenosine-adenosine-thymidine-enhancer-binding protein homologous protein expression. This effect is indicative of an increase in endoplasmic reticulum (ER) stress, and apoptosis signaling including cleavage of caspase-3, caspase-9, poly-adenosine diphosphate-ribose polymerase, and phospho-p53, as well as expression of PRMT3, PRMT4 and fatty acid amide hydrolase (FAAH)1 in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells. In addition, overexpression of PRMT3 or PRMT4 increased the expression of FAAH1 expression, apoptosis, and ER stress signaling in HEI-OC1 cells, whereas PRMT3 or PRMT4 knockdown had the opposite effect. Furthermore, overexpression of FAAH1 increased apoptosis and ER stress, but expression of the PRMTs was unchanged. In addition, a cannabinoid 1 receptor agonist and FAAH inhibitor attenuated apoptosis and ER stress, while cisplatin increased the binding of PRMT3 with FAAH1. In the in vivo experiments, cisplatin was injected intraperitoneally at 6 mg/kg/day into C57BL/6 mice, and 7 days later, this study confirmed that PRMT3 and PRMT4 were upregulated in the organ of Corti of the mice. These results indicate that cisplatin-induced ototoxicity was correlated with PRMT3, PRMT4 and the cannabinoid system, and PRMT3 binding with FAAH1 was increased by cisplatin in HEI-OC1 cells. Therefore, this study suggests that PRMT3 mediates cisplatin-induced ototoxicity via interaction with FAAH1 in vitro and in vivo.

Melatonin attenuates cisplatin-induced acute kidney injury in rats via induction of anti-aging protein, Klotho.

This study investigated the protective effects of melatonin (MT) against cisplatin (CP)-induced acute kidney injury in rats as well as its possible mechanism of action associated with anti-aging protein Klotho. The following four experimental groups were evaluated: vehicle control, CP (7 mg/kg), CP&MT20 (20 mg/kg/day), and CP&MT40 (40 mg/kg/day). The concomitant administration of MT significantly ameliorated CP-induced acute kidney injury in rats, as evidenced by increased kidney weight, increased serum levels of blood urea nitrogen and creatinine, and increased incidence of histopathological alterations with renal tubular cell apoptosis. In addition, MT treatment protected kidney tissue against oxidative damages and significantly upregulated the expression level of Klotho decreased by CP treatment, resulting in reduced phosphorylation of protein kinase B (AKT) and forkhead box O (FOXO) as well as reduced expression levels of B-cell lymphoma 2-associated X protein (Bax) and caspase-3. MT not only partially regulated oxidative stress via AKT/FOXO signaling, but also reduced apoptosis caused by CP by inhibiting the Bax/caspase-3 pathway. Our results indicated that MT could prevent acute kidney injury induced by CP in rats, presumably through upregulating the expression of Klotho, resulting in elevated anti-oxidant and anti-apoptotic properties.

Protective effect of water extract of guibi-tang against pulmonary inflammation induced by cigarette smoke and lipopolysaccharide.

Water extract of guibi-tang (GB), a traditional Chinese, Japanese, and Korean herbal medicine, is used to treat memory impairment, insomnia, and peptic ulcers. The aim of this study was to investigate the protective effects of GB on pulmonary inflammation induced by cigarette smoke (CS) and lipopolysaccharide (LPS). C57BL/6 mice were used to develop a pulmonary inflammation model by exposing them to CS for 1 h per day for 7 days. LPS was intranasally administered to mice under mild anesthesia on day 5. GB was administered 1 h before CS exposure at doses of 50 or 100 mg/kg for 7 days. Our results showed that GB suppressed the CS and LPS induced elevation in inflammatory cell counts in the bronchoalveolar lavage fluid (BALF), with significant reductions in protein, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 levels. Histological studies revealed that GB decreased the inflammatory cell infiltration into lung tissue caused by CS- and LPS-exposure. GB also significantly decreased the CS and LPS-induced expression of inducible nitric oxide synthase (iNOS) in the lung tissue. Taken together, GB effectively attenuated airway inflammation caused by CS and LPS. These results indicate that GB is a potential therapeutic herbal formula for pulmonary inflammatory disease.

Fatal lactic acidosis in hepatitis B virus-associated decompensated cirrhosis treated with tenofovir: A case report.

RATIONALE: Recently tenofovir disoproxil fumarate (TDF) has been widely used as a first-line therapy for chronic hepatitis B (CHB) infection. Although TDF demonstrates successful viral suppression, the possibility of renal failure and lactic acidosis has been proposed with TDF administration, especially in human immunodeficiency virus co-infected patients. However, TDF induced lactic acidosis has never been reported in CHB mono-infected patients. PATIENT CONCERNS: A 59-year-old man received TDF for hepatitis B associated with cirrhosis. After ten days of TDF administration, nausea, vomiting and abdominal pain developed. High anion gap acidosis with elevated lactate level (pH 7.341, pCO2 29.7 mmHg, HCO3- 15.6mmHg, lactate 3.2mmol/L, anion gap 15.4 mEq/L) was developed. DIAGNOSIS: With no infection, normal diagnostic paracentesis, and urinalysis together with high anion gap and increased blood lactate levels suggested lactic acidosis. INTERVENTIONS: TDF was stopped, and haemodialysis was performed to control lactic acidosis. OUTCOMES: Although stopping TDF instantly and treating lactic acidosis using hemodialysis, the patient died. LESSONS: Although, Fatal lactic acidosis is very rare in TDF patient, however, decompensated cirrhotic patients should be closely observed to keep the possibility of lactic acidosis in mind.

RNA activation-independent DNA targeting of the Type III CRISPR-Cas system by a Csm complex.

The CRISPR-Cas system is an adaptive and heritable immune response that destroys invading foreign nucleic acids. The effector complex of the Type III CRISPR-Cas system targets RNA and DNA in a transcription-coupled manner, but the exact mechanism of DNA targeting by this complex remains elusive. In this study, an effector Csm holocomplex derived from Thermococcus onnurineus is reconstituted with a minimalistic combination of Csm1121334151, and shows RNA targeting and RNA-activated single-stranded DNA (ssDNA) targeting activities. Unexpectedly, in the absence of an RNA transcript, it cleaves ssDNA containing a sequence complementary to the bound crRNA guide region in a manner dependent on the HD domain of the Csm1 subunit. This nuclease activity is blocked by a repeat tag found in the host CRISPR loci. The specific cleavage of ssDNA without a target RNA suggests a novel ssDNA targeting mechanism of the Type III system, which could facilitate the efficient and complete degradation of foreign nucleic acids.

Structural features of Cas2 from Thermococcus onnurineus in CRISPR-cas system type IV.

CRISPR-Cas is RNA-based prokaryotic immune systems that defend against exogenous genetic elements such as plasmids and viruses. Cas1 and Cas2 are highly conserved components that play an essential part in the adaptation stage of all CRISPR-Cas systems. Characterization of CRISPR-Cas genes in Thermococcus onnurineus reveals the association of the Cas2 gene with the putative type IV system that lacks Cas1 or its homologous genes. Here, we present a crystal structure of T. onnurineus Cas2 (Ton_Cas2) that exhibits a deep and wide cleft at an interface lined with positive residues (Arg16, Lys18, Lys19, Arg22, and Arg23). The obvious DNA recognizing loops in Cas2 from E. coli (Eco_Cas2) are absent in Ton_Cas2 and have significantly different shapes and electrostatic potential distributions around the putative nucleotide binding region. Furthermore, Ton_Cas2 lacks the hairpin motif at the C-terminus that is responsible for Cas1 binding in Eco_Cas2. These structural features could be a unique signature and indicate an altered functional mechanism in the adaptation stage of Cas2 in type IV CRISPR-Cas systems.

Huntingtin's spherical solenoid structure enables polyglutamine tract-dependent modulation of its structure and function.

The polyglutamine expansion in huntingtin protein causes Huntington's disease. Here, we investigated structural and biochemical properties of huntingtin and the effect of the polyglutamine expansion using various biophysical experiments including circular dichroism, single-particle electron microscopy and cross-linking mass spectrometry. Huntingtin is likely composed of five distinct domains and adopts a spherical α-helical solenoid where the amino-terminal and carboxyl-terminal regions fold to contain a circumscribed central cavity. Interestingly, we showed that the polyglutamine expansion increases α-helical properties of huntingtin and affects the intramolecular interactions among the domains. Our work delineates the structural characteristics of full-length huntingtin, which are affected by the polyglutamine expansion, and provides an elegant solution to the apparent conundrum of how the extreme amino-terminal polyglutamine tract confers a novel property on huntingtin, causing the disease.

Diallyl disulfide attenuates acetaminophen-induced renal injury in rats.

This study investigated the protective effects of diallyl disulfide (DADS) against acetaminophen (AAP)-induced acute renal injury in male rats. We also investigated the effects of DADS on kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL), which are novel biomarkers of nephrotoxicity in renal tissues, in response to AAP treatment. The following four experimental groups were evaluated: (1) vehicle control, (2) AAP (1,000 mg/kg), (3) AAP&DADS, and (4) DADS (50 mg/kg/day). AAP treatment caused acute kidney injury evidenced by increased serum blood urea nitrogen (BUN) levels and histopathological alterations. Additionally, Western blot and immunohistochemistry analysis showed increased expression of KIM-1 and NGAL proteins in renal tissues of AAP-treated rats. In contrast, DADS pretreatment significantly attenuated the AAP-induced nephrotoxic effects, including serum BUN level and expression of KIM-1 and NGAL proteins. Histopathological studies confirmed the renoprotective effect of DADS. The results suggest that DADS prevents AAP-induced acute nephrotoxicity, and that KIM-1 and NGAL may be useful biomarkers for the detection and monitoring of acute kidney injury associated with AAP exposure.

Crystal structure of the Csm1 subunit of the Csm complex and its single-stranded DNA-specific nuclease activity.

The CRISPR-Cas system is the RNA-guided immune defense mechanism in bacteria and archaea. Csm1 belongs to the Cas10 family, which is the common signature protein of the type III system. Csm1 is the largest subunit of the Csm interference complex in the type III-A subtype, which targets foreign DNA or RNA. Here, we report crystallographic and biochemical analyses of Thermococcus onnurineus Csm1, revealing a five-domain organization and single-stranded DNA (ssDNA)-specific nuclease activity associated with the N-terminal HD domain. This domain folds into permuted secondary structures in comparison with the HD domain of Cas3 and contains all the catalytically important residues. It exhibited both endo- and exonuclease activities in an Ni(2+) or Mn(2+)-dependent manner. The narrow width of the active-site cleft appears to restrict the substrate specificity to ssDNA and thus to prevent Csm1 from cleaving double-stranded chromosomal DNA. These data suggest that Csm1 may function in DNA interference by the Csm effector complex.

A novel domain arrangement in a monomeric cyclodextrin-hydrolyzing enzyme from the hyperthermophile Pyrococcus furiosus.

PFTA (Pyrococcus furiosus thermostable amylase) is a hyperthermophilic amylase isolated from the archaeon Pyrococcus furiosus. This enzyme possesses characteristics of both α-amylase- and cyclodextrin (CD)-hydrolyzing enzymes, allowing it to degrade pullulan, CD and acarbose-activities that are absent in most α-amylases-without the transferring activity that is common in CD-hydrolyzing enzymes. The crystal structure of PFTA revealed a unique monomeric subunit with an extended N-terminal region and an N'-domain folded into its own active site-a significantly altered domain configuration relative to that of the conventional dimeric CD-hydrolyzing amylases in glycoside hydrolase family 13. The active site is formed by the interface of the N'-domain and the catalytic domain and exhibits a broad and wide-open geometry without the concave pocket that is commonly found in the active sites of maltogenic amylases. The mutation of a residue (Gly415 to Glu) located at the domain interface between the N'- and catalytic domains yielded an enzyme that produced a significantly higher purity maltoheptaose (G7) from ß-CD, supporting the involvement of this interface in substrate recognition and indicating that this mutant enzyme is a suitable candidate for the production of pure G7. The unique configuration of the active site distinguishes this archaic monomeric enzyme from classical bacterial CD-hydrolyzing amylases and provides a molecular basis for its enzymatic characteristics and for its potential use in industrial applications.

Identification of a novel ligand binding site in phosphoserine phosphatase from the hyperthermophilic archaeon Thermococcus onnurineus.

Phosphoserine phosphatase (PSP) catalyzes the final and irreversible step of L-serine synthesis by hydrolyzing phosphoserine to produce L-serine and inorganic phosphate. Developing a therapeutic drug that interferes with serine production is of great interest to regulate the pathogenicity of some bacteria and control D-serine levels in neurological diseases. We determined the crystal structure of PSP from the hyperthermophilic archaeon Thermococcus onnurineus at 1.8 Å resolution, revealing an NDSB ligand bound to a novel site that is located in a fissure between the catalytic domain and the CAP module. The structure shows a half-open conformation of the CAP 1 module with a unique protruding loop of residues 150-155 that possesses a helical conformation in other structures of homologous PSPs. Activity assays indicate that the enzyme exhibits marginal PSP activity at low temperature but a sharp increase in the k(cat)/K(M) value, approximately 22 fold, when the temperature is increased. Structural and biochemical analyses suggest that the protruding loop in the active site might be an essential component for the regulation of the activity of PSP from hyperthermophilic T. onnurineus. Identification of this novel binding site distantly located from the catalytic site may be exploited for the development of effective therapeutic allosteric inhibitors against PSP activity.

Structural analysis of alpha-L-arabinofuranosidase from Thermotoga maritima reveals characteristics for thermostability and substrate specificity.

An alpha-L-arabinofuranosidase (TmAFase) from Thermotoga maritima MSB8 is a highly thermostable exo-acting hemicellulase that exhibits a relatively higher activity towards arabinan and arabinoxylan, compared with other glycoside hydrolase 51 family enzymes. In the present study, we carried out the enzymatic characterization and structural analysis of TmAFase. Tight domain associations found in TmAFase, such as an inter-domain disulfide bond (Cys306 and Cys476) in each monomer, a novel extended arm (amino acids 374-385) at the dimer interface, and total 12 salt bridges in the hexamer, may account for the thermostability of the enzyme. One of the xylan binding determinants (Trp96) was identified in the active site, and a region of amino acids (374-385) protrudes out forming an obvious wall at the substrate-binding groove to generate a cavity. The altered cavity shape with a strong negative electrostatic distribution is likely related to the unique substrate preference of TmAFase towards branched polymeric substrates.