Salt Bridge Research Articles

Silicon porous disc featured parabolic trough collector functioned with paraffin: Thermal performance study

The advancement of renewable solar energy has potential for industrial heat exchanger applications, and its performance is enhanced by using nanofluid. Besides, the losses of heat during the energy transfer from solar to heat exchanger limit thermal performance and lead to reduced thermal efficiency. The conventional solar system functioning with nanofluid needs to be upgraded with an advanced thermal management system to limit energy loss and enrich the thermal performance of the overall system. The investigation aims to enrich the thermal performance of a parabolic trough solar collector (PTC), which features silicon porous discs and phase change material (PCM-paraffin). During the investigation, the flow of fluid ranged from 100 to 200 LPH with an interval of 50 LPH. Influences of silicon porous disc and phase change material melting phase on fluid temperature, temperature, energy stored, and thermal efficiency of the present system are experimentally investigated, and its values are related to conventional absorber performance without porous material and phase change material. The output results prove the significance of silicon porous and phase change material related to conventional absorber systems. The parabolic solar collector functioned with silicon porous material with phase change material phase on 200LPH spotted superior thermal performance including fluid temperature, PCM temperature, energy stored by phase change material, and average thermal & exergy efficiency of 84.2 °C, 98.5 °C 599.7 kJ, and 73.8 % & 15.1 %. These findings underscore the promising potential of porous medium absorbers in significantly elevating the efficiency of parabolic trough collector systems.

Characterization of NLRP3 inflammasome components in the endangered Chinese giant salamander (Andrias davidianus)

Chinese giant salamander (Andrias davidianus) is the largest extant urodela species and has unique evolutionary position. Studying the immune system of Chinese giant salamander contributes to understanding the evolution of immune systems of vertebrates. The NLR-related protein 3 (NLRP3) inflammasome comprised of NLRP3, ASC and caspase-1 play important roles in the host innate immunity. However, little is know about the NLRP3 inflammasome components in Chinese giant salamander. In this study, the NLRP3, apoptosis-associated speck-like protein (ASC) and caspase-1 (adaNLRP3, adaASC and adaCaspase-1) were characterized from Chinese giant salamander. The proteins of these three genes shared similar motifs and structures with their mammalian counterparts, with a PYD motif, a nucleotide-binding domain (NACHT) motif, and four leucine-rich repeat domain (LRR) motifs identified in adaNLRP3, a pyrin domain (PYD) motif and a caspase recruitment domain (CARD) motif in adaASC, and a CARD motif and a CASc motif in adaCaspase-1. These three genes were constitutively expressed in the skin, heart, lung, kidney, muscle, brain, spleen, and liver of Chinese giant salamander. Following Aeromonas hydrophia infection, all the three genes were up-regulated in various tissues. Molecular docking analysis revealed that the key residues involved in forming the adaNLRP3/adaASC complex were located in the PYD motifs, and that involved in forming the adaASC/adaCaspase-1 complex were located in the CARD motifs. Further analysis revealed that the hydrogen bonds and salt bridges had crucial roles in the formation of adaNLRP3/acaASC and adaASC/adaCaspase-1 complexes. To the best of our knowledge, this is the first report on the NLRP3 inflammasome components in Chinese giant salamander which will be helpful in further understanding the function of the NLRP3 inflammasome and in elucidating its role in the immune response to microbes.

Spectroscopic Relationship between XOD and TAOZHI Total Polyphenols Based on Chemometrics and Molecular Docking Techniques.

Xanthine oxidase (XOD) is a key enzyme that promotes the oxidation of xanthine/hypoxanthine to form uric acid, and the accumulation of uric acid leads to hyperuricaemia. The prevalence of gout caused by hyperuricaemia is increasing year by year. TAOZHI (TZ) can be used for the treatment of rheumatic arthralgia due to qi stagnation and blood stasis and contains a large number of polyphenolic components. The aim of this study was to investigate the relationship between chromatograms and XOD inhibition of 21 batches of TZ total polyphenol extract samples. Chemometric methods such as grey correlation analysis, bivariate correlation analysis, and partial least squares regression were used to identify the active ingredient groups in the total polyphenol extracts of TZ, which were validated using molecular docking techniques. The total polyphenol content contained in the 21 batches did not differ significantly, and all batches showed inhibitory effects on XOD. Spectroeffect correlation analysis showed that the inhibitory effect of TZ on XOD activity was the result of the synergistic effect of multiple components, and the active component groups screened to inhibit XOD were F2 (4-O-Caffeoylquinic acid), F4, and F10 (naringenin). The molecular docking results showed that the binding energies of all nine dockings were lower than -7.5 kcal/mol, and the binding modes included hydrogen bonding, hydrophobic forces, salt bridges, and π-staking, and the small molecules might exert their pharmacological effects by binding to XOD through the residue sites of the amino acids, such as threonine, arginine, and leucine. This study provides some theoretical basis for the development and utilisation of TZ total polyphenols.

Force Field Limitations of All-Atom Continuous Constant pH Molecular Dynamics.

All-atom constant pH molecular dynamics simulations offer a powerful tool for understanding pH-mediated and proton-coupled biological processes. As the protonation equilibria of protein sidechains are shifted by electrostatic interactions and desolvation energies, pK a values calculated from the constant pH simulations may be sensitive to the underlying protein force field and water model. Here we investigated the force field dependence of the all-atom particle mesh Ewald (PME) continuous constant pH (PME-CpHMD) simulations of a mini-protein BBL. The replica-exchange titration simulations based on the Amber ff19SB and ff14SB force fields with the respective water models showed significantly overestimated pK a downshifts for a buried histidine (His166) and for two glutamic acids (Glu141 and Glu161) that are involved in salt-bridge interactions. These errors (due to undersolvation of neutral histidines and overstabilization of salt bridges) are consistent with the previously reported pK a's based on the CHARMM c22/CMAP force field, albeit in larger magnitudes. The pK a calculations also demonstrated that ff19SB with OPC water is significantly more accurate than ff14SB with TIP3P water, and the salt-bridge related pK a downshifts can be partially alleviated by the atom-pair specific Lennard-Jones corrections (NBFIX). Together, these data suggest that the accuracies of the protonation equilibria of proteins from constant pH simulations can significantly benefit from improvements of force fields.

Differential Behavior of Conformational Dynamics in Active and Inactive States of Cannabinoid Receptor 1.

Cannabinoid receptor 1 (CB1) is a G protein-coupled receptor that regulates critical physiological processes including pain, appetite, and cognition. Understanding the conformational dynamics of CB1 associated with transitions between inactive and active signaling states is imperative for developing targeted modulators. Using microsecond-level all-atom molecular dynamics simulations, we identified marked differences in the conformational ensembles of inactive and active CB1 in apo. The inactive state exhibited substantially increased structural heterogeneity and plasticity compared to the more rigidified active state in the absence of stabilizing ligands. Transmembrane helices TM3 and TM7 were identified as distinguishing factors modulating the state-dependent dynamics. TM7 displayed amplified fluctuations selectively in the inactive state simulations attributed to disruption of conserved electrostatic contacts anchoring it to surrounding helices in the active state. Additionally, we identified significant reorganizations in key salt bridge and hydrogen bond networks contributing to the CB1 activation/inactivation. For instance, D213-Y224 hydrogen bond and D184-K192 salt bridge showed marked rearrangements between the states. Collectively, these findings reveal the specialized role of TM7 in directing state-dependent CB1 dynamics through electrostatic switch mechanisms. By elucidating the intrinsic enhanced flexibility of inactive CB1, this study provides valuable insights into the conformational landscape enabling functional transitions. Our perspective advances understanding of CB1 activation mechanisms and offers opportunities for structure-based drug discovery targeting the state-specific conformational dynamics of this receptor.

Disruption of salt bridge interactions in the inter-domain cleft of the tubulin-like protein FtsZ of Escherichia coli makes cells sensitive to the cell division inhibitor PC190723.

FtsZ forms a ring-like assembly at the site of division in bacteria. It is the first protein involved in the formation of the divisome complex to split the cell into two halves, indicating its importance in bacterial cell division. FtsZ is an attractive target for developing new anti-microbial drugs to overcome the challenges of antibiotic resistance. The most potent inhibitor against FtsZ is PC190723, which is effective against all strains and species of Staphylococcus, including the methicillin- and multi-drug-resistant Staphylococcus aureus and strains of Bacillus. However, FtsZs from bacteria such as E. coli, Streptococcus, and Enterococcus were shown to be resistant to this inhibitor. In this study, we provide further evidence that the three pairwise bridging interactions, between residues S227 and G191, R307 and E198 and D299 and R202, between S7, S9, S10 β-strands and the H7 helix occlude the inhibitor from binding to E. coli FtsZ. We generated single, double and triple mutations to disrupt those bridges and tested the effectiveness of PC190723 directly on Z-ring assembly in vivo. Our results show that the disruption of S227-G191 and R307-E198 bridges render EcFtsZ highly sensitive to PC190723 for Z-ring assembly. Ectopic expression of the double mutants, FtsZ S227I R307V results in hypersensitivity of the susceptible E. coli imp4213 strain to PC190723. Our studies could further predict the effectiveness of PC190723 or its derivatives towards FtsZs of other bacterial genera.

Design Glutamate Dehydrogenase for Nonaqueous System by Motifs Reassembly and Interaction Network Analysis.

Glutamate dehydrogenases (GDH) serve as the key regulated enzyme that links protein and carbohydrate metabolism. Combined with motif reassembly and mutation, novel GDHs were designed. Motif reassembly of thermophilic GDH and malate dehydrogenase aims to overcome stability and activity tradeoff in nonaqueous systems. Structural compatibility and dynamic cooperation of the designed AaDHs were studied by molecular dynamics simulation. Furthermore, multipoint mutations improved its catalytic activity for unnatural substrates. Amino acid interaction network analysis indicated that the high density of hydrogen-bonded salt bridges is beneficial to the stability. Finally, the experimental verification determines the kinetics of AaDHs in a nonaqueous system. The activity of Aa05 was increased by 1.78-fold with ionic liquid [EMIM]BF4. This study presents the strategy of a combination of rigid motif assembly and mutations of active sites for robust dehydrogenases with high activity in the nonaqueous system, which overcomes the activity-stability tradeoff effect.

Nitric Oxide Ameliorates the Effects of Hypoxia in Mice by Regulating Oxygen Transport by Hemoglobin.

Xiaoying Zhou, Wenting Su, Quanwei Bao, Yu Cui, Xiaoxu Li, Yidong Yang, Chengzhong Yang, Chengyuan Wang, Li Jiao, Dewei Chen, and Jian Huang. Nitric oxide ameliorates the effects of hypoxia in mice by regulating oxygen transport by hemoglobin. High Alt Med Biol. 25:174-185, 2024.-Hypoxia is a common pathological and physiological phenomenon in ischemia, cancer, and strenuous exercise. Nitric oxide (NO) acts as an endothelium-derived relaxing factor in hypoxic vasodilation and serves as an allosteric regulator of hemoglobin (Hb). However, the ultimate effects of NO on the hematological system invivo remain unknown, especially in extreme environmental hypoxia. Whether NO regulation of the structure of Hb improves oxygen transport remains unclear. Hence, we examined whether NO altered the oxygen affinity of Hb (Hb-O2 affinity) to protect extremely hypoxic mice. Mice were exposed to severe hypoxia with various concentrations of NO, and the survival time, exercise capacity, and other physical indexes were recorded. The survival time was prolonged in the 5 ppm NO (6.09 ± 1.29 minutes) and 10 ppm NO (6.39 ± 1.58 minutes) groups compared with the 0 ppm group (4.98 ± 1.23 minutes). Hypoxia of the brain was relieved, and the exercise exhaustion time was prolonged when mice inhaled 20 ppm NO (24.70 ± 6.87 minutes vs. 20.23 ± 6.51 minutes). In addition, the differences in arterial oxygen saturation (SO2%) (49.64 ± 7.29% vs. 42.90 ± 4.30%) and arteriovenous SO2% difference (25.14 ± 8.95% vs. 18.10 ± 6.90%) obviously increased. In ex vivo experiments, the oxygen equilibrium curve (OEC) left shifted as P50 decreased from 43.77 ± 2.49 mmHg (0 ppm NO) to 40.97 ± 1.40 mmHg (100 ppm NO) and 38.36 ± 2.78 mmHg (200 ppm NO). Furthermore, the Bohr effect of Hb was enhanced by the introduction of 200 ppm NO (-0.72 ± 0.062 vs.-0.65 ± 0.051), possibly allowing Hb to more easily offload oxygen in tissue at lower pH. The crystal structure reveals a greater distance between Asp94β-His146β in nitrosyl -Hb(NO-Hb), NO-HbβCSO93, and S-NitrosoHb(SNO-Hb) compared to tense Hb(T-Hb, 3.7 Å, 4.3 Å, and 5.8 Å respectively, versus 3.5 Å for T-Hb). Moreover, hydrogen bonds were less likely to form, representing a key limitation of relaxed Hb (R-Hb). Upon NO interaction with Hb, hydrogen bonds and salt bridges were less favored, facilitating relaxation. We speculated that NO ameliorated the effects of hypoxia in mice by promoting erythrocyte oxygen loading in the lung and offloading in tissues.

Comparative analysis of carrageenan/ovalbumin and carrageenan oligosaccharide/ovalbumin complexes

The saccharides ι-carrageenan (ι-CG) and ι-carrageenan oligosaccharides (ι-CO) exhibit different molecular chain lengths and charge intensities, which are pivotal determinants of their interactions with ovalbumin (OVA). This study investigated the interaction mechanisms between OVA and ι-CG as well as between OVA and ι-CO using experimental methods and molecular docking. The results of zeta potential showed that the strongest electrostatic interaction occurred at an OVA/ι-CG ratio of 100:13 (−1.59 ± 0.41 mV) and an OVA/ι-CO ratio of 100:10 (−1.32 ± 0.30 mV). The OVA/ι-CG complexes showed higher turbidity (1.63 ± 0.08 cm−1). Furthermore, Fourier transform infrared spectroscopy showed that ι-CG significantly altered the secondary structure of OVA, whereas ι-CO did not affect it. Fluorescence spectroscopy also verified the interactions in the OVA/ι-CG and OVA/ι-CO complexes. Both complexes exhibited shear-thinning behaviour; the largest storage modulus (G′) and loss modulus (G″) were observed at 100:13 and 100:10 ratios for OVA/ι-CG OVA/ι-CO samples, respectively. ι-CG induced OVA to form more loosely clumped aggregates, whereas OVA and ι-CO formed compact granular aggregates when observed using confocal scanning laser microscopy. Molecular docking results showed that more salt bridges were formed between ι-CG and OVA than between ι-CO and OVA. A schematic model was established to elucidate the effects of ι-CG and ι-CO on OVA. This study provides instructions for designing innovative food systems based on different charge intensities and chain lengths of saccharides.

Discovery of the potent covalent inhibitor with an acrylate warhead for SARS-CoV-2 3CL protease

COVID-19 has caused severe consequences in terms of public health and economy worldwide since its outbreak in December 2019. SARS-CoV-2 3C-like protease (3CLpro), crucial for the viral replications, is an attractive target for the development of antiviral drugs. In this study, several kinds of Michael acceptor warheads were utilized to hunt for potent covalent inhibitors against 3CLpro. Meanwhile, novel 3CLpro inhibitors with the P3-3,5-dichloro-4-(2-(dimethylamino)ethoxy)phenyl moiety were designed and synthesized which may form salt bridge with residue Glu166. Among them, two compounds 12b and 12c exhibited high inhibitory activities against SARS-CoV-2 3CLpro. Further investigations suggested that 12b with an acrylate warhead displayed potent activity against HCoV-OC43 (EC50 = 97 nM) and SARS-CoV-2 replicon (EC50 = 45 nM) and low cytotoxicity (CC50 > 10 μM) in Huh7 cells. Taken together, this study devised two series of 3CLpro inhibitors and provided the potent SARS-CoV-2 3CLpro inhibitor (12b) which may be used for treating coronavirus infections.

Novel, tightly structurally related N-myristoyltransferase inhibitors display equally potent yet distinct inhibitory mechanisms

N-myristoyltransferases (NMTs) catalyze essential acylations of N-terminal alpha or epsilon amino groups of glycines or lysines. Here, we reveal that peptides tightly fitting the optimal glycine recognition pattern of human NMTs are potent prodrugs relying on a single-turnover mechanism. Sequence scanning of the inhibitory potency of the series closely reflects NMT glycine substrate specificity rules, with the lead inhibitor blocking myristoylation by NMTs of various species. We further redesigned the series based on the recently recognized lysine-myristoylation mechanism by taking advantage of (1) the optimal peptide chassis and (2) lysine side chain mimicry with unnatural enantiomers. Unlike the lead series, the inhibitory properties of the new compounds rely on the protonated state of the side chain amine, which stabilizes a salt bridge with the catalytic base at the active site. Our study provides the basis for designing first-in-class NMT inhibitors tailored for infectious diseases and alternative active site targeting.

In-Situ Electrolyte for Electrosynthesis: Scalable Anodically-Enabled One-Pot Sequence from Aldehyde to Isoxazol(in)es.

Electrochemical transformations are considered a green alternative to classical redox chemistry as it eliminates the necessity for toxic and waste producing redox reagents. Typical electrochemical reactions require the addition of a so-called supporting electrolyte - a salt bridge - and other additives, such as hexafluorisopropanol, to enhance conductivity and reaction outcomes, respectively. However, this is often accompanied by an increase in the amount of produced waste. Here, we report an "in-situ electrolyte" concept for facile, transition-metal-free, additive-free one-pot electrochemical preparation of isoxazol(in)es, important scaffolds for biologically active natural and synthetic molecules, from the respective aldehydes. The protocol utilizes no halogenated solvents and no external oxidants, while salt side-products provide the ionic conductivity necessary for the electrosynthesis. The electrolysis is performed in an undivided cell, using the state-of-the-art electrodes for the chlor-alkali industry dimensionally stable and scalable mixed metal oxide anode and platinized titanium anode of high durability. The cascade transformation comprises the condensation of aldehyde to oxime followed by its anodic oxidation and subsequent intra- and/or intermolecular [3+2] cycloadditions with an appropriate dipolarophile. Chemical yields up to 97%, and good Faradaic efficiency, scalability, and stability are observed for most substrates in a broad scope.

Designing and Optimization of Microbial Fuel Cell for the production of Bioelectricity

MFC technology is a new type of technology which generates electricity from organic waste with the help of microorganisms by using their metabolic activities. It has now become a promising and efficient technology that converts waste to energy. The present study demonstrates the production of bioelectricity from vegetable waste. Double chambered microbial fuel cell was constructed which was connected with the salt bridge. Bacillus megaterium was used in the MFC which proved to be an efficient microbe for the production of bioelectricity. The maximum power generated was 50Mw using 1% CMC.

Hook loop dynamics engineering transcended the barrier of activity-stability trade-off and boosted the thermostability of enzymes

The improvement of enzyme thermostability often accompanies the decreased activity due to the loss of the key regions' flexibility. As a representative structure, unlocking the potential of loop dynamics will not only provide new ideas for stabilization strategies, but also help to deepen the understanding of the relationship between enzyme structural dynamics and function. In this study, a creative “hook loop dynamics engineering” (HLoD) strategy was successfully proposed for simultaneously improving the thermostability and maintaining activity of the model enzyme, Candida Antarctica lipase B. A small and smart mutant library involving five key residues located at the “hook loop” was meticulously identified and systematically investigated and thus yielded a five-point multiple mutant M1 (L147S/T244P/S250P/T256D/N292D), demonstrating a remarkable 7.0-fold increase in thermostability at 60 °C compared to the wild-type (WT). Furthermore, the activity of M1 remained comparable to that of WT, effectively transcending the barrier of activity-stability trade-off. Molecular dynamics simulations revealed that the precise regulation of hook loop dynamics via intermolecular interactions, such as salt bridges and hydrogen bonding, curbed the excessive flexibility of the pivotal regions α5 and α10 at high temperatures, thus driving the substantial enhancement of the thermostability of M1. Refining the dynamics of the flexible region via HLoD, which transcended the barrier of activity-stability trade-off, exhibited to be a robust and potentially universal strategy for designing enzymes with outstanding thermostability and activity.

Arginine-solubilized lipoic acid-induced β-sheets of silk fibroin-strengthened hydrogel for postoperative rehabilitation of breast cancer

Breast cancer is the most common cancer among women worldwide, and adjuvant radiotherapy (RT) following tumor removal is one of the most commonly used treatments for breast cancer. However, the high risk of tumor recurrence and inevitable radiation skin injury after RT remain fatal problems, seriously challenging the patient's postoperative rehabilitation. Herein, a multifunctional poly (lipoic acid)-based hydrogel is constructed through one-step heating the mixture of α-lipoic acid (LA)/arginine (Arg)/silk fibroin (SF), without introducing any non-natural molecules. The multiple synergistic interactions among LA, Arg, and SF not only enhance the solubilization of LA in aqueous systems but also stabilize poly(lipoic acid) through strong salt bridge hydrogen bonds and ionic hydrogen bonds. Intriguingly, the LA-based surfactant induced β-sheet transformation of SF can further modulate the bulk strength of the hydrogel. Regulating the content of LA in hydrogels not only allows efficient control of hydrogel bioactivity but also enables the evolution of hydrogels from injectable forms to adhesive patches. Based on the different biological activities and forms of hydrogels, they can be implanted internally or applied externally on the mice's skin, achieving simultaneous prevention of tumor recurrence post-surgery and assistance in treating radiation-induced skin damage after radiotherapy.

Identification of salty peptides from enzymolysis extract of oyster by peptidomics and virtual screening

Salty peptide as an important sodium substitute, which could reduce the risk of cardiovascular disease caused by excessive sodium intake. In this study, novel salty peptides were prepared and identified from enzymolysis extract of oysters by peptitomic identification, virtual screening and solid phase synthesis. Additionally, molecular simulation was used to study the taste mechanism of salty peptides. 316 peptides were identified in the enzymatic hydrolysates of oysters. 6 peptides, selected through virtual screening, were synthesized using solid-phase synthesis, and EK, LFE, LEY and DR were confirmed to possess a pleasing salty taste through electronic tongue evaluation. Molecular docking results indicated that these 4 peptides could enter the binding pocket within the transmembrane channel-like 4 (TMC4) cavity, wherein salt bridges, hydrogen bonds and attractive charges were the main binding forces. This study provides a rapid screening method for salty peptides in sea food products but possibly applied for other sources.

Sustainable recycling of aluminum scraps to recycled aerospace-grade 7075 aluminum alloy sheets

The production of aerospace-grade aluminum alloy sheet is characterized by stringent demands, resulting in a low yield rate. The processing of this material generates considerable amounts of highly alloyed scrap, complicating its recycling due to the challenge of maintaining melt cleanliness. This study employed an aerospace-grade melt refining system to purify the recycled 7075 alloy melt obtained from comprehensive scrap remelting. The melt's cleanliness was assessed using Porous Disc Filtration Analysis (PoDFA) and Liquid Metal Cleanliness Analyzer (LiMCA) and Alscan. The microstructure of the ingots and sheets was examined through Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD), whereas the mechanical properties of recycled sheets were evaluated and benchmarked against those of primary sheet at an aerospace-certified testing facility. The findings indicate that the recycled 7075 sheet meets aviation standards, with no significant differences in microstructure or performance when compared to primary sheet. Furthermore, the study highlights the economic benefits of recycling scrap, revealing a potential cost saving of $4210.8 per ton of recycled sheet. The findings presented herein offer a theoretical framework and empirical evidence supporting the development of a recycling system for aerospace scraps and the certification of airworthiness for recycled aerospace aluminum alloy.

Mechanistic insights into lanthipeptide modification by a distinct subclass of LanKC enzyme that forms dimers

Naturally occurring lanthipeptides, peptides post-translationally modified by various enzymes, hold significant promise as antibiotics. Despite extensive biochemical and structural studies, the events preceding peptide modification remain poorly understood. Here, we identify a distinct subclass of lanthionine synthetase KC (LanKC) enzymes with distinct structural and functional characteristics. We show that PneKC, a member of this subclass, forms a dimer and possesses GTPase activity. Through three cryo-EM structures of PneKC, we illustrate different stages of peptide PneA binding, from initial recognition to full binding. Our structures show the kinase domain complexed with the PneA core peptide and GTPγS, a phosphate-bound lyase domain, and an unconventional cyclase domain. The leader peptide of PneA interact with a gate loop, transitioning from an extended to a helical conformation. We identify a dimerization hot spot and propose a “negative cooperativity” mechanism toggling the enzyme between tense and relaxed conformation. Additionally, we identify an important salt bridge in the cyclase domain, differing from those in in conventional cyclase domains. These residues are highly conserved in the LanKC subclass and are part of two signature motifs. These results unveil potential differences in lanthipeptide modification enzymes assembly and deepen our understanding of allostery in these multifunctional enzymes.

Chemical modification of hyaluronan oligosaccharides differentially modulates hyaluronan–hyaladherin interactions

The glycosaminoglycan hyaluronan (HA) is a ubiquitous, nonsulfated polysaccharide with diverse biological roles mediated through its interactions with HA-binding proteins (HABPs). Most HABPs belong to the Link module superfamily, including the major HA receptor, CD44, and secreted protein TSG-6, which catalyzes the covalent transfer of heavy chains from inter-α-inhibitor onto HA. The structures of the HA-binding domains (HABDs) of CD44 (HABD_CD44) and TSG-6 (Link_TSG6) have been determined and their interactions with HA extensively characterized. The mechanisms of binding are different, with Link_TSG6 interacting with HA primarily via ionic and CH-π interactions, whereas HABD_CD44 binds solely via hydrogen bonds and van der Waals forces. Here, we exploit these differences to generate HA oligosaccharides, chemically modified at their reducing ends, that bind specifically and differentially to these target HABPs. Hexasaccharides (HA6AN) modified with 2- or 3-aminobenzoic acid (HA6-2AA, HA6-3AA) or 2-amino-4-methoxybenzoic acid (HA6-2A4MBA), had increased affinities for Link_TSG6 compared to unmodified HA6AN. These modifications did not increase the affinity for CD44_HABD. A model of HA6-2AA (derived from the solution dynamic 3D structure of HA4-2AA) was docked into the Link_TSG6 structure, providing evidence that the 2AA-carboxyl forms a salt bridge with Arginine-81. These modeling results informed a second series of chemical modifications for HA oligosaccharides, which again showed differential binding to the two proteins. Several modifications to HA4 and HA6 were found to convert the oligosaccharide into substrates for heavy chain transfer, whereas unmodified HA4 and HA6 are not. This study has generated valuable research tools to further understand HAbiology.

An effective, novel and low-cost proton exchange membrane for microbial fuel cell-based bioelectricity production

Microbial Fuel Cells (MFCs) are a substitute for fossil-fuel-based electricity generation. They are innovative bioelectrochemical systems that use microbial catalysts to convert organic waste directly into electrical energy. However, MFCs face several commercialization challenges, including expensive Proton Exchange Membranes (PEMs), making them unaffordable. The present research aims to develop cost-effective, environmentally friendly, high-performance PEM to make MFC technology more viable. The study analyzed using MFCs with different PEMs with native microflora and Serratia marcescens (AATB1) as biocatalysts to produce bioelectricity and treat septic tank wastewater (STWW). The experiment included a control group with sterile STWW. The study involves fabricating and characterizing the optimized Novel Cement Supported Conductive Salts PEM (NCSCS PEM) using SEM, TGA, and EIS techniques. The commercial Nafion 117 and salt bridge were used to compare NCSCS PEM in MFCs. The anode biofilm was investigated using CV, CLSM, and SEM. The MFCs with Nafion 117, NCSCS PEM, and Salt bridge produced power densities of 126.6 ± 1.06 mW/m2, 204.04 ± 0.87 mW/m2, and 188.26 ± 1.13 mW/m2, respectively. Moreover, Our study shows a greater PEM cost reduction with commercial Nafion 117 PEM in terms of consumed cost of $7.04, $0.21, and $2.41 for making MFCs with Nafion 117 (9 cm2), NCSCS PEM (15 cm3) (with 97.02 % reduced cost) and salt bridge (15 cm3) (with 65.77 % reduced cost) respectively. Our MFC setup cost was reduced by 70.29 % by replacing Nafion 117 with durable NCSCS PEM. Using our cost-effective, better-performing, durable NCSCS in MFC makes the MFC technology or any other technology that needs PEM feasible on a larger scale.