Effects of terminal modification on the catalytic efficiency and thermostability of Brucella melitensis 7α‑hydroxysteroid dehydrogenase

Brucella melitensis 7α-hydroxysteroid dehydrogenase(Bm7α-HSDH)catalyzes the oxidation of chenodeoxycholic acid to 7-oxolithocholic acid.In this work,we investigated the effects of terminal modification(His-tags location and terminal truncation)on its catalytic efficiency and thermostability.Compared with C-terminal His-tagged Bm7α-HSDH(C-Bm7α-HSDH),N-Bm7α-HSDH showed a 3.6-fold higher kcat and a 1.3-fold lower Km,resulting in a 7.0-fold higher kcat/Km value toward chenodeoxycholic acid.Circular dichroism spectroscopy indicated that the melting temperature of N-Bm7α-HSDH(46.13℃)was 3.0℃lower than that of C-Bm7α-HSDH(49.13℃).N-Bm7α-HSDH produced 7-oxolithocholic acid in the highest yield of 96.7%in 4 h,whereas the C-Bm7α-HSDH gave 96.4%in 10 h.Moreover,amino acids truncation and His-tag cleave experiments confirmed the C-terminal residues played key roles in catalytic functions.Molecular dynamics simulations further indicated C-terminal His-tagged modification could deform the substrate-binding region to disrupt the enzyme–substrate interactions and catalytic motion.However,the N-terminal His-tag hardly affected the catalytic efficiency due to its location far from the active site of the enzyme.This study provides structural insights into the terminus modifications of hydroxysteroid dehydrogenase on steroid substrate recognition and stabilization,thus affecting its catalytic functions.

Advanced semiconductor catalyst designs for the photocatalytic reduction of CO_(2)

Using clean solar energy to reduce CO_(2)into value-added products not only consumes the over-emitted CO_(2)that causes environmental problems,but also generates fuel chemicals to alleviate energy crises.The photocatalytic CO_(2)reduction reaction(PCO_(2)RR)relies on the semiconductor photocatalysts that suffer from high recombination rate of the photo-generated carriers,low light harvesting capability,and low stability.This review explores the recent discoveries on the novel semiconductors for PCO_(2)RR,focusing on the rational catalyst design strategies(such as surface engineering,band engineering,hierarchical structure construction,single-atom catalysts,and biohybrid catalysts)that promote the catalytic performance of semiconductor catalysts on PCO_(2)RR.The advanced characterization techniques that contribute to understanding the intrinsic properties of the photocatalysts are also discussed.Lastly,the perspectives on future challenges and possible solutions for PCO_(2)RR are presented.

Comparative Analysis of Gas Emissions from a Vehicle Running on Ethanol and Natural Gas Fuel

It is known that the transport sector has a fundamental importance in the modem society, as the economic development is directly linked to mobility. Over the years, the transport became linked to different environmental problems, which can be detached greenhouse gases emissions in the atmosphere, where in recent decades can be perceived the intensification and targeting of efforts in research and development of new technologies to reduce the levels of greenhouse gases emissions in the atmosphere. In this context, it can be highlighted the modem systems of electronic engine management, new automotive catalysts and the use of renewable fuels which contribute to reducing the environmental impact. This research had, as its purpose, the analysis of fuels characteristics used for testing, comparative analysis of gas emissions from a motor vehicle running on ethanol or natural gas fuels according to NBR 6601 and conducting tests to estimate the maximum catalytic efficiency. For the implementation of trial, a flex vehicle was installed in a chassis dynamometer equipped with a gas analyzer, in order that before the completion of the urban driving cycle, were determined the content of hydrocarbons corrected, carbon monoxide corrected, carbon dioxide and oxygen present in gas emissions from the engine. The research concluded that： the performance analysis for characterization of fuel showed consistent with ANP specifications; after tests performances, it can be stated that natural gas fuel was the fuel which had the highest content of hydrocarbons and carbon monoxide corrected, while ethanol had the highest amount of carbon dioxide and oxygen residue present in gas emissions; before a comparative analysis, the vehicle catalyst showed the best performance for reducing the content of hydrocarbon corrected present in exhaustion gases when it worked with natural gas fuel and showed maximum efficiency of 100% to reduce the content of carbon monoxide corrected for both fuels. Before this, it can be stated that the vehicle catalyst showed satisfactory performance, achieving good reduction levels of greenhouse gases emissions.

Evaluation of arsenic pollution in field-contaminated soil at the soil’s actual pH

The pollution and ecological risks posed by arsenic(As)entering the soil are the major environmental challenges faced by human beings.Soil phosphatase can serve as a useful indicator for assessing As contamination under specific soil pH conditions.However,the study of phosphatase kinetics in long-term field As-contaminated soil remains unclear,presenting a significant obstacle to the monitoring and evaluation of As pollution and toxicity.The purpose of this study was to determine phosphatase activity and explore enzyme kinetics in soils subjected to long-term field As contamination.Results revealed that the soil phosphatase activity varied among the tested soil samples,depending on the concentrations of As.The relationship between total As,As fractions and phosphatase activity was found to be significant through negative exponential function fitting.Kinetic parameters,including maximum reaction velocity(Vmax),Michaelis constant(Km)and catalytic efficiency(V_(max)/K_(m)),ranged from 3.14×10^(−2)–53.88×10^(−2) mmol/(L·hr),0.61–7.92 mmol/L,and 0.46×10^(−2)–11.20×10^(−2) hr−1,respectively.Vmax and Vmax/Km of phosphatase decreased with increasing As pollution,while Km was less affected.Interestingly,Vmax/Km showed a significant negative correlationwith all As fractions and total As.The ecological doses(ED10)for the complete inhibition and partial inhibition models ranged from0.22–70.33 mg/kg and 0.001–55.27 mg/kg,respectively,indicating that V_(max)/K_(m) can be used as an index for assessing As pollution in field-contaminated soil.This study demonstrated that the phosphatase kinetics parameters in the soil’s pH system were better indicators than the optimal pH for evaluating the field ecotoxicity of As.

A new surface catalytic model for silica-based thermal protection material for hypersonic vehicles

Silica-based materials are widely employed in the thermal protection system for hypersonic vehicles, and the investigation of their catalytic characteristics is crucially important for accurate aerothermal heating prediction. By analyzing the disadvantages of Norman＇s high and low temperature models, this paper combines the two models and proposes an eight-reaction combined surface catalytic model to describe the catalysis between oxygen and silica surface. Given proper evaluation of the parameters according to many references, the recombination coefficient obtained shows good agreement with experimental data. The catalytic mechanisms between oxygen and silica surface are then analyzed. Results show that with the increase of the wall temperature, the dominant reaction contributing to catalytic coefficient varies from Langmuir Hinshelwood （LH） recombination （Tw 〈 620 K） to Eley Rideal （ER） replacement （620 K 〈 Tw 〈 1350 K）, and then to 02 desorption （Tw 〉 1350 K）. The surface coverage of chemisorption areas varies evidently with the dominant reactions in the high temperature （HT） range, while the surface coverage of physisorption areas varies within quite low temperature （LT） range （Tw 〈 250 K）. Recommended evaluation of partial parameters is also given.

Green-synthesized gold nanoparticles from Plumeria alba flower extract to augment catalytic degradation of organic dyes and inhibit bacterial growth

Bio-inspired eco-friendly gold nanoparticles were synthesized by a green method using aqueous Plume- ria alba flower extract （PAFE）. The use of 1% and 5% concentrations of PAFE resulted in two different sizes of P. alba gold nanoparticles, PAGNPsl and PAGNPs2, with surface plasmon resonance （SPR） peaks at 552 and 536 nm, respectively. Size-controlled formation of gold nanoparticles was indicated by the SPR shift observed with increasing concentration of PAFE. The accurate size and morphology of PAGNPs I and PAGNPs2 were determined by transmission electron microscope （TEM） analysis is found to be 28 ＋ 5.6 and 15.6 4-3.4 nm, respectively, and those are spherical in shape. The antibacterial activity of PAGNPsl and PAGNPs2 was tested against Escherichia coil; the small-sized PAGNPs2 exhibited better antibacterial activity with a 16-mm zone of inhibition at a concentration of 400 txg/mL. Furthermore, the catalytic activity of PAGNPsl and PAGNPs2 was analyzed on six hazardous dyes; PAGNPs2 exhibited more pro- nounced catalytic activity than PAGNPsl. Among all of the dyes, 4-nitrophenol was most rapidly degraded to 4-aminophenol by PAGNPs2 within 5 min. The mechanism of catalysis in the presence of PAGNPsl and PAGNPs2 can be described as an electron transfer process from donor NaBH4 to an acceptor. The facile green synthesis of such eco-friendly nanoparticles in bulk suggests this method has potential industrial applications.

Cloning,expression and improvement of catalytic activity of alginate lyase by site-directed mutation

Alginate lyase mainly produces active alginate oligosaccharides(AOS)by degrading alginate viaβ-elimination process.In this study,the Pseudoalteromonas sp.Alg6B alginate lyase-encoding gene alg6B-7 from polysaccharide lyase(PL)-7 family was successfully cloned,sequenced,expressed in Escherichia coli.Based on rational design and amino acid sequence alignment of the alginate lyase from various sources,four positive mutants were obtained.The specific enzyme activities of four mutants I62A,A99K,V132S,and L157T were 38.84%,42.85%,75.8%and 51.83%higher than that of the wild enzyme,respectively.The K_(cat)/K_(m) values of the four mutants were both increased,and the catalytic efficiency of V132S was 1.92-fold higher than that of the wild enzyme,especially.The rational design that was employed in this study achieved the dramatic improvement of catalytic activity,which may provide the application potential in industrial production.

MECE:基于深度神经网络及进化分析提高糖苷水解酶的催化效率

糖苷水解酶(glycoside hydrolases,GHs)在各个行业广泛应用,其需求量不断增加.然而,如何提高酶的催化效率仍然是一个挑战.本文开发了基于深度神经网络和分子进化的策略(MECE)预测提高糖苷水解酶催化活性的突变体.作者首先从CAZy数据库中收集整理了119个糖苷水解酶家族的蛋白序列,建立了能够识别糖苷水解酶家族和功能残基的深度学习模型DeepGH,通过10倍交叉验证结果显示DeepGH模型的预测准确率为96.73%.随后利用梯度加权类激活图谱(Grad-CAM)方法提取分类相关特征,结合序列进化信息对突变体进行设计最后获得了具有7个氨基酸突变位点的壳聚糖酶突变体CHIS1754-MUT7.实验结果表明,CHIS1754-MUT7的k_(cat)/K_m是野生型的23.53倍.该策略计算效率高,实验成本低,具有显著的优势,为酶催化效率的智能设计提供了一种新的途径,具有广泛的应用前景.

Thermo-sensitive Porous Polymer Membrane-immobilized Cellulose as a Switchable Enzyme Reactor for Tuning Its Enzymolysis via Variation Temperature

Immobilization of enzymes onto porous membranes has attracted considerable attention in recent years.However,enhancing the enzymolysis efficiency of the resulting enzyme reactors by varying the environmental conditions poses a great challenge.In this work,poly(styrene-maleic anhydride-N,N-dimethylacrylamide)was prepared and utilized to construct a thermo-sensitive porous polymer membrane-based enzyme reactor(TS-PPMER)after cellulase was immobilized onto the support by covalent bonding.The catalytic activity of the nano-reactor was evaluated by measuring the yield of the product,glucose,at different temperatures with carboxymethylcellulose as the substrate.Interestingly,the polymer chains coiled and formed numerous nano-pores at a high temperature,which induced the confine effect and greatly boosted the enzymolysis efficiency of TS-PPMER.Furthermore,the proposed TS-PPMER was applied in the hydrolysis of green plant leaves in Epipremnum aureum.This work shows great potential in obtaining biological resources by an environmentally friendly approach using smart polymer-based nano-reactors.

Improvement of the activity and thermostability of l‑threonine aldolase from Pseudomonas putida via tailoring of the active sites lining the binding pocket

l-threonine aldolases catalyze the conversion of glycine and aldehydes to synthesizeβ-hydroxy-α-amino acids with unsatisfactory enzyme activity.Here,we expressed the l-threonine aldolase from Pseudomonas putida KT2440(l-PpTA)in Escherichia coli BL21(DE3)and improved the activity and thermostability by protein engineering.Five amino acid residues(Ser10,His89,Asp93,Arg177,and Arg321)located in the substrate-binding pocket were selected and for mutation.Eight mutants(D93A,D93G,D93M,D93F,D93S,D93Q,D93Y and D93H)with increased enzyme activity were identified and their k_(cat)/K_(M)values showed about 1-7-fold higher than wild-type.Among all the variants,D93H showed the highest catalytic efficiency with 2925 and 4515 s^(−1)mM^(−1)of k_(cat)/K_(M)values toward l-threonine and l-allo-threonine,respectively.In addition,circular dichroism spectrum exhibited that the melting temperature of D93H(54.2℃)was 5℃higher than wild-type(49.2℃).Molecular dynamics simulations illustrated that the D93H variant shortens the distance between the imidazole group of H93 and the hydroxyl group of substrate,which facilitated the proton extraction and promote the enzymatic reaction.This work affords a candidate for the synthesis ofβ-hydroxy-α-amino acids with improved catalytic efficiency and thermostability and provides structural insights into the l-TA family by protein engineering.

Advance in glycosyltransferases, the important bioparts for production of diversified ginsenosides

Ginsenosides are a series of glycosylated triterpenoids predominantly originated from Panax species with multiple pharmacological activities such as anti-aging, mediatory effect on the immune system and the nervous system. During the biosynthesis of ginsenosides, glycosyltransferases play essential roles by transferring various sugar moieties to the sapogenins in contributing to form structure and bioactivity diversified ginsenosides, which makes them important bioparts for synthetic biology-based production of these valuable ginsenosides. In this review, we summarized the functional elucidated glycosyltransferases responsible for ginsenoside biosynthesis, the advance in the protein engineering of UDP-glycosyltransferases(UGTs) and their application with the aim to provide in-depth understanding on ginsenoside-related UGTs for the production of rare ginsenosides applying synthetic biology-based microbial cell factories in the future.

Highly Efficient and Thermal Robust Cobalt Complexes for 1,3-Butadiene Polymerization

A family of highly bulky bis(salicylaldiminate)Co(Ⅱ)complexes bearing cavity-like conformations are disclosed herein.Due to their unique bulky nature around the cobalt atoms that are reflected from space-filling models and the buried volume percentages,obviously longer bond distances of Co―N and Co―O are revealed from those complexes.Moreover,because of these well-protected active species,the cobalt complexes are able to catalyze 1,3-butadiene polymerization in high yields at extreme low catalyst concentrations,revealing a ultra high catalytic efficiency.At a ratio of 50000,all the complexes can afford polybutadiene with yields higher than 90%.Furthermore,the highly steric bulkiness of the ligand can also significantly enhance the thermostability of the active species.At temperature of 80-120°C,the complexes are able to successfully maintain high activities,giving polymer yields up to 90%.

Vacancies-rich CoAl monolayer layered double hydroxide as efficient superoxide dismutase-like nanozyme

With the extensive development of nanozymes in recent years,catalytic efficiency has been considered as the Gordian knot that restricts the further applications of nanozyme.Moreover,the usage of layered double hydroxides(LDHs)as antioxidant nanozymes for scavenging reactive oxygen species(ROS)has not been studied.Herein,we report a vacancies-rich monolayer cobalt-alumina LDH nanosheet(m-CoAl-LDH)through a facile direct synthesis method as an efficient nanozyme with superoxide dismutase(SOD)-like activity.The m-CoAl-LDH exhibits a record-breaking catalytic efficiency with the catalytic constant(Kcat)as high as 4.33×10^(11)M^(−1)·s−1.Elucidated by the experimental and theoretical studies,the abundant oxygen and metal vacancies were existed in the single layer for the outstanding performance owing to the increased active sites.In addition,density functional theory(DFT)calculations further reveal the significant role of synergistic effect of oxygen and metal vacancies in reducing the adsorption energy of superoxide(O_(2)^(•−)),which improves the catalytic performance.The m-CoAl-LDH nanosheets were applied in cells to relieving the oxidative damage caused by O_(2)^(•−)in mitochondria.Such vacancy-rich monolayer CoAl-LDH nanosheets represent the first example of LDH nanozyme with specific SOD-like activity as well as record high catalytic efficiency,which may provide deeper insight into efficient nanozyme design by defect-engineering.

Hydrothermal synthesis of crystalline α-/β-MnO_(2) nanorods via γ-MnOOH nanorod precursors

The crystalline α-MnO_(2) and β-MnO_(2) nanorods have been successfully prepared via a facile hydrothermal method from γ-MnOOH nanorods precursor,respectively.The samples were characterized by means of X-ray diff raction(XRD),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM),field emission scanning electron microscope(FESEM)and Fourier transformed infrared spectra(FTIR).The morphology and structure of γ-MnOOH nanorods precursors have a great influence on the crystal structure of the obtained products.The α-MnO_(2) nanorods are prepared from the 100℃ γ-MnOOH precursor,while the β-MnO_(2) nanorods are obtained from the 150℃ γ-MnOOH precursor,respectively.Besides,the catalytic activity of the prepared α-MnO_(2) and β-MnO_(2) nanorods for the H2O2 decomposition has been investigated comparatively,and the latter shows better catalytic activity.