New Insights into the Cooperativity and Dynamics of Dimeric Enzymes.

A survey of protein databases indicates that the majority of enzymes exist in oligomeric forms, with about half of those found in the UniProt database being homodimeric. Understanding why many enzymes are in their dimeric form is imperative. Recent developments in experimental and computational techniques have allowed for a deeper comprehension of the cooperative interactions between the subunits of dimeric enzymes. This review aims to succinctly summarize these recent advancements by providing an overview of experimental and theoretical methods, as well as an understanding of cooperativity in substrate binding and the molecular mechanisms of cooperative catalysis within homodimeric enzymes. Focus is set upon the beneficial effects of dimerization and cooperative catalysis. These advancements not only provide essential case studies and theoretical support for comprehending dimeric enzyme catalysis but also serve as a foundation for designing highly efficient catalysts, such as dimeric organic catalysts. Moreover, these developments have significant implications for drug design, as exemplified by Paxlovid, which was designed for the homodimeric main protease of SARS-CoV-2.

Mitigation of the corrosion-causing Desulfovibrio desulfuricans biofilm using an organic silicon quaternary ammonium salt in alkaline media simulated concrete pore solutions.

Organic silicon quaternary ammonium salt (OSA), an environmentally friendly naturally occurring chemical, was used as a bacteriostatic agent against sulphate-reducing bacteria (SRB) on a 20SiMn steel surface in simulated concrete pore solutions (SCP). Four different media were used: No SRB (NSRB), No SRB and OSA (NSRB + OSA), With SRB (WSRB), With SRB and OSA (WSRB + OSA). After biofilm growth for 28 days, optimized sessile SRB cells survived at the high pH of 11.35 and as a result these cells caused the breakdown of the passive film due to the metabolic activities of the SRB. Corrosion prevention results showed that the OSA was effective in mitigating the growth of the sessile SRB cells and reduced corrosion in the SCP. These results were further confirmed by scanning electron microscope images, energy dispersive X-ray analysis, confocal-laser scanning microscopy, X-ray photoelectron spectroscopy and corrosion testing using electrochemical analysis.

The enhanced effect of activated sludge attached to the roots of Pistia stratiotes on nutrient removal for secondary effluent.

Aquatic plants are widely used for treating wastewater treatment plant secondary effluent. During this process, some residual activated sludge in the secondary effluent is intercepted and attaches to the plant roots. However, the effect of the attached activated sludge on nutrient removal in secondary effluent has up to now been unknown. Aiming at this problem, this investigation was conducted to compare the nutrient removal rates in secondary effluent by washed Pistia stratiotes (washed batch) and Pistia stratiotes with activated sludge attached to the roots (study batch). Extracellular polymeric substances (EPS) from the activated sludge attached to the roots were extracted and characterized by three-dimensional excitation emission matrix (3D-EEM) fluorescence spectroscopy. The results showed that the nutrient removal rates in the study batch were better than that in the washed batch. The 3D-EEM results showed that the protein content of EPS increased during the experiment, indicating the growth of microorganisms in the attached activated sludge. Our work demonstrated the enhanced effect of activated sludge attached to the roots of Pistia stratiotes on the removal of pollutants in secondary effluent, which is useful to guide the practical engineering of secondary effluent treatment.

Application of Y-shaped, coated self-expandable metallic stents for anastomotic stenosis after gastrojejunostomy (Billroth II).

BACKGROUND: Anastomotic stenosis is an infrequent but life-threatening complication after gastrojejunostomy (Billroth II). Tubular or single tubular stents have limited efficacy due to the particular anatomy. PURPOSE: To assess the feasibility of a Y-shaped, fully-coated, self-expandable, metallic stent (SEMS) for anastomotic stenosis after gastrojejunostomy (Billroth II). MATERIAL AND METHODS: Between January 2008 and August 2014, 14 patients (10 with gastric carcinoma and four with duodenal ulcers) had anastomotic stenoses following Billroth II reconstructions. Eight patients with gastric cancer had tumor recurrence near the anastomosis; two had benign strictures. The four duodenal ulcer patients had benign stenoses. An integrated Y-shaped, fully coated SEMS was designed to accord with the anatomy of residual gastrojejunal anastomotic strictures. Fourteen stents were inserted under fluoroscopic control. Follow-up was at 1, 3, 9, and 12 months, and then annually. RESULTS: All 14 stents were inserted successfully at the first attempt with a technical success rate of 100%. After stenting, abdominal symptoms resolved in all patients. All patients were followed up for 4-27 months (mean, 13.9 months). One of the eight recurrent cases died of multiple tumor metastases and liver failure after 7 months, without obstruction symptoms. In all six patients with benign anastomotic stenosis, the stents were removed successfully without complication and with no evidence of restenosis based on clinical evaluation and imaging. CONCLUSION: A Y-shaped, fully-coated SEMS proved to be a feasible and minimally invasive procedure for treating anastomotic stenosis after gastrojejunostomy (Billroth II).

Cellulose separation from ramie bone by one step process with green hydrogen peroxide-citric acid.

Ramie bone (RB), an agricultural waste generated in the textile industry, is a vastly productive renewable natural resource with the potential to be used as a source of cellulose. In this study, ramie bone cellulose (RB-CE) was obtained in one step using a simple and ecologically friendly hydrogen peroxide-citric acid (HPCA) treatment procedure that avoided the use of halogenated reagents and strong acids while also streamlining the treatment processes. Various analytical methods were used to investigate the chemical composition and structure, crystallinity, morphology, thermal properties, surface area and hydration properties of cellulose separated at different treatment temperatures. HPCA successfully removed lignin and hemicellulose from RB, according to chemical composition analysis and FTIR. RB-CE had a type I cellulose crystal structure, and the crystallinity improved with increasing treatment temperature, reaching 72.51 % for RB-CE90. The RB-CE showed good thermal stability with degradation temperatures ranging from 294.2 °C to 319.1 °C. Furthermore, RB-CE had a high water/oil binding capacity, with RB-CE90 having WHC and OBC of 9.68 g/g and 7.24 g/g, respectively. The current work serves as a model for the environmentally friendly and convenient extraction of cellulose from biomass, and the cellulose obtained can be employed in the field of food and composite materials.

Right bronchopleural fistula treated with a novel, Y-shaped, single-plugged, covered, metallic airway stent.

BACKGROUND: Bronchopleural fistula (BPF) is an infrequent but life-threatening complication after pneumonectomy. The incidence of BPF reported in the literature varies from 0.3% to 20%. PURPOSE: To determine the feasibility and efficacy of using Y-shaped, single-plugged, covered, metallic stents to treat right bronchopleural fistulas. MATERIAL AND METHODS: We have designed a Y-shaped, single-plugged, covered, self-expandable, metallic airway stent to fit the specific anatomy of the right main bronchus. The stent has a main tube and two branches, resembling an inverted "Y". One of the branches is closed (plugged) and bullet-shaped; the other one tubular and open. The entire stent is encased in a nitinol wire mesh. Stent size can be individualized using multislice spiral computed tomography (MSCT) measurements of the airways. Under fluoroscopic guidance, we have implanted 15 Y-shaped stents in 15 patients with right bronchopleural fistulas. RESULTS: Stent insertion was successful in all patients. All fistulas were successfully closed immediately after stent placement. Follow-up was performed for 1-34 months. Positive clinical outcomes were seen in 13 of 15 patients. Two patients died of intractable pulmonary infection and multiorgan failure. The fistula completely healed and the stent could be removed in five patients; however, two of them were left with a small, aseptic, residual right lung cavity. The remaining eight patients are still alive with the stent in situ. CONCLUSION: The placement of Y-shaped, single-plugged, covered, self-expandable metallic airway stents seems to be a feasible and safe method for the treatment of bronchopleural fistulas involving the right main bronchus. This stent is a promising therapeutic alternative for bronchopleural fistulas involving the right main bronchus.

A multicenter study on the prevalence of adults and children seeking orthodontic treatment at high risk of obstructive sleep apnea.

OBJECTIVE: To investigate the prevalence of adults and children seeking orthodontic treatment at high risk of obstructive sleep apnea (OSA) and pediatric OSA (POSA) and its association with demographic variables. METHODS: One hundred-eleven adults and 105 children were consecutively recruited from three centers. The Epworth Sleepiness Scale (ESS) and ESS for Children and Adolescents were used for Risk stratifications for OSA and POSA. RESULTS: The prevalence of patients seeking orthodontic treatment at high risk of OSA/POSA was 27.8%, where 26.1% were adults, and 29.5% were children. High risk for OSA/POSA was not associated with gender, ethnicity, age, Body Mass Index, or neck circumference. CONCLUSION: Approximately 26% of adults and 30% of children seeking orthodontic care were at high risk for OSA and POSA. Screening for OSA and POSA among adults and children seeking orthodontic treatment is imperative.

Molecular crowding creates an essential environment for the formation of stable G-quadruplexes in long double-stranded DNA.

Large numbers of guanine-rich sequences with potential to form G-quadruplexes have been identified in genomes of various organisms. Such sequences are constrained at both ends by long DNA duplex with a complementary strand in close proximity to compete for duplex formation. G-quadruplex/duplex competition in long double-stranded DNA has rarely been studied. In this work, we used DMS footprinting and gel electrophoresis to study G-quadruplex formation in long double-stranded DNA derived from human genome under both dilute and molecular crowding condition created by PEG. G-quadruplex formation was observed in the process of RNA transcription and after heat denaturation/renaturation under molecular crowding condition. Our results showed that the heat denaturation/renaturation treatment followed by gel electrophoresis could provide a simple method to quantitatively access the ability of G-quadruplex formation in long double-stranded DNA. The effect of K(+) and PEG concentration was investigated and we found that stable G-quadruplexes could only form under the crowding condition with PEG at concentrations near the physiological concentration of biomass in living cells. This observation reveals a physical basis for the formation of stable G-quadruplexes in genome and supports its presence under the in vivo molecular crowding condition.

Crevice Corrosion Behavior of Alloy 690 in High-Temperature Aerated Chloride Solution.

Crevice corrosion behavior of Alloy 690 in high-temperature aerated chloride solution was studied using a self-designed crevice device. The SEM, EDS, XRD, and XPS analyses results indicated that the oxide films outside the crevice consisted of Ni-Cr oxides containing a small amount of hydroxides, and the oxide films on crevice mouth consisted of a (Ni,Fe)(Fe,Cr)2O4 spinel oxides outer layer and a Cr(OH)3 inner layer, and the oxide films inside the crevice consisted of a α-CrOOH outer layer and a Cr(OH)3 inner layer. When crevice corrosion occurred, the hydrolysis of Cr3+ led to the formation of Cr(OH)3 inside the crevice, and caused the pH value of crevice solution to decrease, and Cl- migrated from outside the crevice into inside the crevice due to electrical neutrality principle and accumulation. When the water chemistry inside the crevice reached the critical value of active dissolution of metal, the active dissolution of metal inside the crevice occurred. In addition, (Ni,Fe)(Fe,Cr)2O4 spinel oxides on the crevice mouth were formed by the deposition of metal ions migrated from inside the crevice. The mechanism of crevice corrosion and the formation mechanism of oxide films at different regions were also discussed.

Sequestration and transport of lignin monomeric precursors.

Lignin is the second most abundant terrestrial biopolymer after cellulose. It is essential for the viability of vascular plants. Lignin precursors, the monolignols, are synthesized within the cytosol of the cell. Thereafter, these monomeric precursors are exported into the cell wall, where they are polymerized and integrated into the wall matrix. Accordingly, transport of monolignols across cell membranes is a critical step affecting deposition of lignin in the secondarily thickened cell wall. While the biosynthesis of monolignols is relatively well understood, our knowledge of sequestration and transport of these monomers is sketchy. In this article, we review different hypotheses on monolignol transport and summarize the recent progresses toward the understanding of the molecular mechanisms underlying monolignol sequestration and transport across membranes. Deciphering molecular mechanisms for lignin precursor transport will support a better biotechnological solution to manipulate plant lignification for more efficient agricultural and industrial applications of cell wall biomass.

Kinetic and thermodynamic control of G-quadruplex folding.

A matter of speed: when allowed to fold in a K(+)/poly(ethylene glycol) solution, the guanine (G)-rich strand of vertebrate telomere DNA forms a parallel/antiparallel G-quadruplex, which is a (3+1) hybrid, within microseconds before slowly transforming into the parallel one within hours. Thus, the conformation that a G-quadruplex initially adopts under physiological conditions may not be the one it adopts at the equilibrium state.

Storage stability of inhalable, controlled-release powder formulations of ciprofloxacin nanocrystal-containing liposomes.

Novel inhalable and controlled release powder formulations of ciprofloxacin nanocrystals inside liposomes (CNL) were recently developed. In the present study, the storage stability of CNL powders consisting of lyoprotectant (i.e. sucrose or lactose), lipids, ciprofloxacin (CIP), and magnesium stearate or isoleucine was investigated. These powders were produced by spray drying, collected in a dry box at <15% relative humidity (RH), then stored at room temperature and either 4 or 20 %RH. Liposomal integrity, CIP encapsulation efficiency (EE), in vitro drug release (IVR), aerosol performance, and solid-state properties were examined over six months. Sucrose CNL powder exhibited consistent liposomal integrity, aerosol performance, and controlled release of CIP over six months of storage at 4 %RH. However, storage of the powder at 20 %RH for the same period caused sucrose crystallization and consequently a significant drop in EE and aerosol performance (p-values < 0.05), along with the IVR of CIP becoming similar to that of the non-crystalline CIP liposomal dispersions (f2 > 50). Lactose CNL maintained superior aerosol performance over the six months irrespective of the storage RH. However, liposomal instability occurred at both RHs within the first month of storage with a significant drop in EE and an increase in liposome size (p-values < 0.05). Moreover, the IVR assay of CIP from lactose CNL showed a less controlled release and a substantial difference (f2 < 50) from its initial value after six months regardless of the storage RHs. In conclusion, dry powder inhalers of CNL were physiochemically stable in sucrose lyoprotectant when stored below 4 %RH at room temperature for six months.

An orally delivered microbial cocktail for the removal of nitrogenous metabolic waste in animal models of kidney failure.

Patients with kidney failure commonly require dialysis to remove nitrogenous wastes and to reduce burden to the kidney. Here, we show that a bacterial cocktail orally delivered in animals with kidney injury can metabolize blood nitrogenous waste products before they diffuse through the intestinal mucosal barrier. The microbial cocktail consists of three strains of bacteria isolated from faecal microbiota that metabolize urea and creatinine into amino acids, and is encapsulated in calcium alginate microspheres coated with a polydopamine layer that is selectively permeable to small-molecule nitrogenous wastes. In murine models of acute kidney injury and chronic kidney failure, and in porcine kidney failure models, the encapsulated microbial cocktail significantly reduced urea and creatinine concentrations in blood, and did not lead to any adverse effects.

Reduced or diminished stabilization of the telomere G-quadruplex and inhibition of telomerase by small chemical ligands under molecular crowding condition.

Telomere DNA in human cells shortens during each round of DNA replication. In cancer cells, telomere shortening is compensated by telomerase or the alternative lengthening of telomere (ALT) mechanism to maintain cell division potential. The G-rich strand of telomere DNA can fold into a G-quadruplex structure and disrupt these two processes. Therefore, stabilization of the G-quadruplex by chemical ligands is emerging as a promising anticancer strategy. So far, in vitro studies on such ligands are exclusively carried out in dilute solutions. However, the intracellular environment is highly crowded with biomolecules. How G-quadruplex ligands behave under molecular crowding condition is critical for their in vivo anticancer effect. In this work, we studied several ligands for their ability to stabilize the telomere G-quadruplex and inhibit telomerase under both dilute and crowding conditions. Surprisingly, the ligands became significantly less effective or even lost the ability to stabilize the G-quadruplex and inhibit telomerase under crowding conditions. Our data attributed this consequence to the decreased binding affinity of ligands to the G-quadruplex as a result of reduced water activity and increased viscosity of the medium associated with molecular crowding. This effect is irrelevant to and overweighs the influences from other factors such as the G-quadruplex structure, cation, and ligand species. Our work illustrates a possibility that molecular crowding inside cells may reduce or limit the potency of ligands although they may be effective in dilute solution, thus strongly arguing for the necessity of evaluating ligands under more physiologically relevant conditions and designing drugs with this concern in mind.

Efficient gene delivery targeted to the brain using a transferrin-conjugated polyethyleneglycol-modified polyamidoamine dendrimer.

The blood-brain barrier (BBB) poses great difficulties for gene delivery to the brain. To circumvent the BBB, we investigated a novel brain-targeting gene vector based on the nanoscopic high-branching dendrimer, polyamidoamine (PAMAM), in vitro and in vivo. Transferrin (Tf) was selected as a brain-targeting ligand conjugated to PAMAM via bifunctional polyethyleneglycol (PEG), yielding PAMAM-PEG-Tf. UV and nuclear magnetic resonance (NMR) spectroscopy were used to evaluate the synthesis of vectors. The characteristics and biodistribution of gene vectors were evaluated by fluorescent microscopy, flow cytometry, and a radiolabeling method. The transfection efficiency of vector/DNA complexes in brain capillary endothelial cells (BCECs) was evaluated by fluorescent microscopy and determination of luciferase activity. The potency of vector/DNA complexes was evaluated by using frozen sections and measuring tissue luciferase activity in Balb/c mice after i.v. administration. UV and NMR results demonstrated the successful synthesis of PAMAM-PEG-Tf. This vector showed a concentration-dependent manner in cellular uptake study and a 2.25-fold brain uptake compared with PAMAM and PAMAM-PEG in vivo. Transfection efficiency of PAMAM-PEG-Tf/DNA complex was much higher than PAMAM/DNA and PAMAM-PEG/DNA complexes in BCECs. Results of tissue expression experiments indicated the widespread expression of an exogenous gene in mouse brain after i.v. administration. With a PAMAM/DNA weight ratio of 10:1, the brain gene expression of the PAMAM-PEG-Tf/DNA complex was approximately 2-fold higher than that of the PAMAM/DNA and PAMAM-PEG/DNA complexes. These results suggested that PAMAM-PEG-Tf can be exploited as a potential nonviral gene vector targeting to brain via noninvasive administration.

Interpreting microbiologically assisted cracking with Ee-pH diagrams.

Although many mechanisms have been proposed to explain the microbiologically assisted cracking (MAC) of steel and copper, a theoretical interpretation is necessary. In this paper, we attempt to give a theoretical interpretation of sulfate/nitrate reducing bacteria (SRB/NRB)-assisted cracking using Ee-pH diagrams. Under the combined actions of SRB/NRB and external stress, the cell potential (Ecell) and the corrosion current density of the corrosion reaction increase, such that the corrosion reactions become more thermodynamically favorable. This is the nature of MAC. Nitrate is a far more potent oxidant than sulfate, and thus, the NRB-assisted cracking of iron is a more thermodynamically favorable process than the SRB-assisted cracking. Furthermore, the thermodynamic interpretation is attempted to implicate into the classical stress corrosion cracking mechanisms of pipeline steel.

Influence of fluoride and chloride on corrosion behavior of NiTi orthodontic wires.

The influence of fluoride and chloride ions on the corrosion behavior of nearly equiatomic nickel-titanium orthodontic wires was studied using conventional electrochemical measurement methods, including corrosion potential, potentiodynamic and cyclic potentiodynamic polarization measurements. In addition, scanning electron microscopy was employed to observe the surface morphology before and after the test. All the electrochemical parameters are analyzed based on the sample standard deviations. The results indicated that NiTi alloy is primarily susceptible to localized corrosion when exposed to a solution containing chloride, while it is susceptible to general corrosion when subjected to a solution containing fluoride. Furthermore, the synergistic interaction of fluoride and chloride on corrosion of NiTi alloy is associated with their respective molar concentrations.

Stress corrosion cracking of NiTi in artificial saliva.

OBJECTIVES: This paper aimed to study the mechanism of the cracking of orthodontic NiTi wire. METHODS: Two orthodontic NiTi wires were subjected: (1) optical and scanning electron microscopy (SEM) to observe the fracture surface; (2) energy dispersive X-ray spectroscopy to determine the composition of the surface product; (3) anodic polarization to remove the surface product. Samples of NiTi alloy were subjected to the constant loading test to study the stress corrosion cracking (SCC) behavior of NiTi shape memory alloy in artificial saliva. RESULTS: The results showed that there were three typical areas at the fracture surface of NiTi orthodontic wire. Area '1' was a tool-made notch. Crack initiated from the root of this notch and propagated to form Area '2', which was perpendicular to the wire axis and covered by surface film. This film consisted of Na, K, Cl, P, S and O except Ni and Ti. The cracking process of NiTi alloy under the constant loading test depended on the pH of saliva and applied stress. The crack length was about 262microm, the longest at 300MPa and pH 3.0. SIGNIFICANCE: A tool-made notch in orthodontic NiTi wires can cause SCC. At high stress and low pH, this NiTi alloy was most sensitive to cracking.

Biological evaluation of silver nanoparticles incorporated into chitosan-based membranes.

AIM: To evaluate the antibacterial potential and biological performance of silver nanoparticles in chitosan-based membranes. MATERIALS & METHODS: Electrospun chitosan/poly(ethylene oxide) membranes with different amounts of silver nanoparticles were evaluated for antibacterial properties and cytotoxicity in vitro and for tissue response in a rabbit subcutaneous model. RESULTS: The nanoparticles displayed dose-dependent antibacterial properties against Porphyromonas gingivalis and Fusobacterium nucleatum, without showing noticeable cytotoxicity. The membranes with silver nanoparticles evoked a similar inflammatory response compared with the membranes without silver nanoparticles. CONCLUSION: The antibacterial effect, combined with the findings on cyto- and biocompatibility warrants further investigation to the usefulness of chitosan/poly(ethylene oxide) membranes with silver nanoparticles, for clinical applications like guided tissue regeneration.

Screening for serum biomarkers in patients with chronic hepatitis B with hepatitis B surface antigen seroclearance, following pegylated interferon alpha therapy.

Chronic hepatitis B (CHB) is one of the most common infectious disease worldwide and a leading cause of death. Hepatitis B surface antigen (HBsAg) has previously been proven to be a steady biomarker that may be used to predict clinical outcomes. The amount of circulating HBsAg has been reported to reflect the number of infected hepatocytes. An advantage of pegylated interferon alpha (peg-IFN-α) is that as a finite course of therapy, it can potentially lead to sustained disease remission in subsequent decades. HBsAg seroclearance can reportedly be achieved in some hepatitis B patients treated with peg-IFN-α; this is a major advantage of IFN-α, as compared with nucleoside analogue treatment. In the present study, a random phage display peptide library was used to screen for potential serum peptide biomarkers in predicting which patients with CHB would exhibit HBsAg seroclearance, following 48 weeks of peg-IFN-α therapy. A total of 30 patients with CHB who achieved HBsAg seroclearance following peg-IFN-α therapy and an additional 30 age-, gender-, hepatitis B e antigen (HBeAg) status- and hepatitis B virus genotype-matched patients with CHB without HBsAg seroclearance following peg-IFN-α therapy, were enrolled as a discovery cohort. In the discovery/screening phase, 17/20 of the randomly selected phage clones, exhibited a specific reaction with purified sera immunoglobulin G from the HBsAg clearance group, and 13/17 positive phage clones came from the same phage clone, with the inserted peptide sequence ETCRASCINESA (named IFNC1). In the validation phase, phage-ELISA results showed that the positive reaction rate of the IFNC1 peptide phage clone was 92.0% with the HBsAg seroclearance group (n=50), which was significantly higher, as compared with the randomly selected HBsAg non-clearance group (12.0%, n=50) and the healthy control group (8.0%, n=50). In conclusion, the newly identified mimic peptide IFNC1 showed a high predictive validity HBsAg seroclearance in patients with CHB, following peg-IFN-α therapy. Therefore IFNC1 may be a potential serum biomarker, which could be used to predict the treatment outcomes of peg-IFN-α therapy.