Molecular-Level Insight into Impact of Additives on Film Formation and Molecular Packing in Y6-based Organic Solar Cells.

Additive engineering is widely utilized to optimize film morphology in active layers of organic solar cells (OSCs). However, the role of additive in film formation and adjustment of film morphology remains unclear at the molecular level. Here, taking high-efficiency Y6-based OSC films as an example, this work thus employs all-atom molecular-dynamics simulations to investigate how introduction of additives with different π-conjugation degree thermodynamically and dynamically impacts nanoscale molecular packings. These results demonstrate that the van der Waals (vdW) interactions of the Y6 end groups with the studied additives are strongest. The larger the π-conjugation degree of the additive molecules, the stronger the vdW interactions between additive and Y6 molecules. Due to such vdW interactions, the π-conjugated additive molecules insert into the neighboring Y6 molecules, thus opening more space for relaxation of Y6 molecules to trigger more ordered packing. Increasing the interactions between the Y6 end groups and the additive molecules not only accelerates formation of the Y6 ordered packing, but also induces shorter Y6-intermolecular distances. This work reveals the fundamental molecular-level mechanism behind film formation and adjustment of film morphology via additive engineering, providing an insight into molecular design of additives toward optimizing morphologies of organic semiconductor films.

Tension Induced Photoluminescence Enhancement in an Organic Single Crystal.

Organic single crystals possess distinct advantages due to their highly ordered molecular structures, resulting in improved stability, enhanced carrier mobility, and superior optical characteristics. However, their mechanical rigidity and brittleness impede the applications in flexible and wearable optoelectronic devices. Here, photoluminescence (PL) emission from 2,6-diphenylanthracene (DPA) single crystals is studied under tensile strain, which shows PL enhancement by more than two times with a strain of ≈1.42%. Such a tension induced PL enhancement is reversible, exhibiting no clear optical degradations during 100 cycles of bending and recovery processes. Theoretical calculations reveal that the deformation of molecular structure under strain induces a decrease of the dihedral between anthracene and benzene moieties in DPA molecules. Further, the increased molecular conjugation enhances the molecular oscillator strength, leading to the brightened PL emission. Meanwhile, with the decreased dihedral, the molecular vibrations in DPA crystals are suppressed, which can reduce the non-radiative decay rate. In contrast, no tension induced PL enhancement is observed in polycrystalline DPA thin films as the strain can be released via the grain boundaries. This study highlights the superior optical performance of DPA single crystals under strain field, which will provide new possibilities for DPA-based flexible devices.

Frenkel and Charge-Transfer Excitonic Couplings Strengthened by Thiophene-Type Solvent Enables Binary Organic Solar Cells with 19.8% Efficiency.

Overcoming the trade-off between short-circuited current (Jsc) and open-circuited voltage (Voc) is important to achieving high-efficiency organic solar cells (OSCs). Previous works modulated energy gap between Frenkel local exciton (LE) and charge-transfer (CT) exciton, which is served as driving force of exciton splitting. Differently, our current work focuses on modulation of LE-CT excitonic coupling (tLE-CT) via a simple but effective strategy that the 2-chlorothiophene (2Cl-Th) solvent is utilized in treatment of OSC active-layer films. The results of our experimental measurements and theoretical simulations demonstrated that 2Cl-Th solvent initiates the tighter intermolecular interactions with non-fullerene acceptor in comparison with that of traditional chlorobenzene solvent, thus suppressing the acceptor's over-aggregation and retarding the acceptor crystallization with reduced trap. Importantly, the resulted shorter distances between donor and acceptor molecules in the 2Cl-Th treated blend efficiently strengthen tLE-CT, which not only promotes the exciton splitting but also reduces non-radiative recombination. The champion efficiencies of 19.8% (small-area) with a superior operational reliability (T80: 586 hours) and 17.0% (large-area) were yielded in 2Cl-Th treated cells. This work provided a new insight into modulating the exciton dynamics to overcome the trade-off between Jsc and Voc, which can productively promote the development of OSC field.

Spin-coated and vacuum-processed hole-extracting self-assembled multilayers with H-aggregation for high-performance inverted perovskite solar cells.

We report a highly crystalline self-assembled multilayer (SAMUL) that is fundamentally different from the conventional monolayer or disordered bilayer used for hole-extraction in inverted perovskite solar cells (PSCs). The SAMUL can be easily formed on ITO substrate to form better surface coverage for enhancing the performance and stability of PSCs. A detailed structure-property-performance relationship of molecules used for SAMUL is established through a systematic study of their crystallinity, molecular packing, and hole-transporting properties. These SAMULs are rationally optimized by varying their molecular structures and deposition through thermal evaporation or spin-coating for fabricating PSCs. The CbzNaphPPA-based SAMUL was chosen for fabricating inverted PSCs due to its highest crystallinity and hole mobility derived from the ordered H-aggregation, which resulted in a remarkably high fill factor of 86.45%. This enables a very impressive power conversion efficiency (PCE) of 26.07% to be achieved along with excellent device stability (94% of its initial PCE retained after continuous operation for 1200 h under 1-sun irradiation at maximum power point at 65°C). Additionally, a record-high PCE of 23.50% could be achieved by adopting a thermally evaporated SAMUL. This greatly simplifies and broadens the scope for SAM to be used for large-area devices on diverse substrates.

Production of Salvianic Acid A from l-DOPA via Biocatalytic Cascade Reactions.

Salvianic acid A (SAA), as the main bioactive component of the traditional Chinese herb Salvia miltiorrhiza, has important application value in the treatment of cardiovascular diseases. In this study, a two-step bioprocess for the preparation of SAA from l-DOPA was developed. In the first step, l-DOPA was transformed to 3,4-dihydroxyphenylalanine (DHPPA) using engineered Escherichia coli cells expressing membrane-bound L-amino acid deaminase from Proteus vulgaris. After that, the unpurified DHPPA was directly converted into SAA by permeabilized recombinant E. coli cells co-expressing d-lactate dehydrogenase from Pediococcus acidilactici and formate dehydrogenase from Mycobacterium vaccae N10. Under optimized conditions, 48.3 mM of SAA could be prepared from 50 mM of l-DOPA, with a yield of 96.6%. Therefore, the bioprocess developed here was not only environmentally friendly, but also exhibited excellent production efficiency and, thus, is promising for industrial SAA production.

Food-grade γ-aminobutyric acid production by immobilized glutamate decarboxylase from Lactobacillus plantarum in rice vinegar and monosodium glutamate system.

OBJECTIVES: γ-amino butyric acid (GABA) is a non-protein amino acid, considered a potent bioactive compound. This study focused on biosynthesis of food-grade GABA by immobilized glutamate decarboxylase (GAD) from Lactobacillus plantarum in the rice vinegar and monosodium glutamate (MSG) reaction system. RESULTS: The gene encoding glutamate decarboxylase (GadB) from L. plantarum has been heterologously expressed in Lactococcus lactis and biochemically characterized. Recombinant GadB existed as a homodimer, and displayed maximal activity at 40 °C and pH 5.0. The Km value and catalytic efficiency (kcat/Km) of GadB for L-Glu was 22.33 mM and 62.4 mM-1 min-1, respectively, with a specific activity of 24.97 U/mg protein. Then, purified GadB was encapsulated in gellan gum beads. Compared to the free enzyme, immobilized GadB showed higher operational and storage stability. Finally, 9.82 to 21.48 g/L of GABA have been acquired by regulating the amounts of catalyst microspheres ranging from 0.5 to 0.8 g (wet weight) in 0.8 mL of the designed rice vinegar and MSG reaction system. CONCLUSIONS: The method of production GABA by immobilized GadB microspheres mixed in the rice vinegar and MSG reaction system is introduced herein for the first time. Especially, the results obtained here meet the increased interest in the harnessing of biocatalyst to synthesize food-grade GABA.

Parallel Strategy Increases the Thermostability and Activity of Glutamate Decarboxylase.

Glutamate decarboxylase (GAD; EC 4.1.1.15) is a unique pyridoxal 5-phosphate (PLP)-dependent enzyme that specifically catalyzes the decarboxylation of L-glutamic acid to produce γ-aminobutyric acid (GABA), which exhibits several well-known physiological functions. However, glutamate decarboxylase from different sources has the common problem of poor thermostability that affects its application in industry. In this study, a parallel strategy comprising sequential analysis and free energy calculation was applied to identify critical amino acid sites affecting thermostability of GAD and select proper mutation contributing to improve structure rigidity of the enzyme. Two mutant enzymes, D203E and S325A, with higher thermostability were obtained, and their semi-inactivation temperature (T5015) values were 2.3 °C and 1.4 °C higher than the corresponding value of the wild-type enzyme (WT), respectively. Moreover, the mutant, S325A, exhibited enhanced activity compared to the wild type, with a 1.67-fold increase. The parallel strategy presented in this work proved to be an efficient tool for the reinforcement of protein thermostability.

A Single Mutation Increases the Thermostability and Activity of Aspergillus terreus Amine Transaminase.

Enhancing the thermostability of (R)-selective amine transaminases (AT-ATA) will expand its application in the asymmetric synthesis of chiral amines. In this study, mutual information and coevolution networks of ATAs were analyzed by the Mutual Information Server to Infer Coevolution (MISTIC). Subsequently, the amino acids most likely to influence the stability and function of the protein were investigated by alanine scanning and saturation mutagenesis. Four stabilized mutants (L118T, L118A, L118I, and L118V) were successfully obtained. The best mutant, L118T, exhibited an improved thermal stability with a 3.7-fold enhancement in its half-life (t1/2) at 40 °C and a 5.3 °C increase in T5010 compared to the values for the wild-type protein. By the differential scanning fluorimetry (DSF) analysis, the best mutant, L118T, showed a melting temperature (Tm) of 46.4 °C, which corresponded to a 5.0 °C increase relative to the wild-type AT-ATA (41.4 °C). Furthermore, the most stable mutant L118T displayed the highest catalytic efficiency among the four stabilized mutants.

Lactobacillus brevis CGMCC 1306 glutamate decarboxylase: Crystal structure and functional analysis.

Glutamate decarboxylase (GAD), which is a unique pyridoxal 5-phosphate (PLP)-dependent enzyme, can catalyze α-decarboxylation of l-glutamate (L-Glu) to γ-aminobutyrate (GABA). The crystal structure of GAD in complex with PLP from Lactobacillus brevis CGMCC 1306 was successfully solved by molecular-replacement, and refined at 2.2 Šresolution to an Rwork factor of 18.76% (Rfree = 23.08%). The coenzyme pyridoxal 5-phosphate (PLP) forms a Schiff base with the active-site residue Lys279 by continuous electron density map, which is critical for catalysis by PLP-dependent decarboxylase. Gel filtration showed that the active (pH 4.8) and inactive (pH 7.0) forms of GAD are all dimer. The residues (Ser126, Ser127, Cys168, Ile211, Ser276, His278 and Ser321) play important roles in anchoring PLP cofactor inside the active site and supporting its catalytic reactivity. The mutant T215A around the putative substrate pocket displayed an 1.6-fold improvement in catalytic efficiency (kcat/Km) compared to the wild-type enzyme (1.227 mM-1 S-1 versus 0.777 mM-1 S-1), which was the highest activity among all variants tested. The flexible loop (Tyr308-Glu312), which is positioned near the substrate-binding site, is involved in the catalytic reaction, and the conserved residue Tyr308 plays a vital role in decarboxylation of L-Glu.

Improving thermostability of (R)-selective amine transaminase from Aspergillus terreus through introduction of disulfide bonds.

To improve the thermostability of (R)-selective amine transaminase from Aspergillus terreus (AT-ATA), we used computer software Disulfide by Design and Modelling of Disulfide Bonds in Proteins to identify mutation sites where the disulfide bonds were most likely to form. We obtained three stabilized mutants (N25C-A28C, R131C-D134C, M150C-M280C) from seven candidates by site-directed mutagenesis. Compared to the wild type, the best two mutants N25C-A28C and M150C-M280C showed improved thermal stability with a 3.1- and 3.6-fold increase in half-life (t1/2 ) at 40 °C and a 4.6 and 5.1 °C increase in T5010 . In addition, the combination of mutant R131C-D134C and M150C-M280C displayed the largest shift in thermostability with a 4.6-fold increase in t1/2 at 40 °C and a 5.5 °C increase in T5010 . Molecular dynamics simulation indicated that mutations of N25C-A28C and M150C-M280C lowered the overall root mean square deviation for the overall residues at elevated temperature and consequently increased the protein rigidity. The stabilized mutation of R131C-D134C was in the region of high mobility and on the protein surface, and the disulfide bond constraints the flexibility of loop 121-136.

Disease resistance features of the executor R gene Xa7 reveal novel insights into the interaction between rice and Xanthomonas oryzae pv. oryzae.

Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is a widespread and destructive disease in rice production. Previously, we cloned an executor R gene, Xa7, which confers durable and broad-spectrum resistance to BB. Here, we further confirmed that the transcription activator-like effector (TALE) AvrXa7 in Xoo strains could directly bind to the effector-binding element (EBE) in the promoter of the Xa7 gene. Other executor R genes (Xa7, Xa10, Xa23, and Xa27) driven by the promoter of the Xa7 gene could be activated by AvrXa7 and trigger the hypersensitive response (HR) in tobacco leaves. When the expression of the Xa23 gene was driven by the Xa7 promoter, the transgenic rice plants displayed a similar resistance spectrum as the Xa7 gene, demonstrating that the disease resistance characteristics of executor R genes are mainly determined by their induction patterns. Xa7 gene is induced locally by Xoo in the infected leaves, and its induction not only inhibited the growth of incompatible strains but also enhanced the resistance of rice plants to compatible strains, which overcame the shortcomings of its race-specific resistance. Transcriptome analysis of the Xa7 gene constitutive expression in rice plants displayed that Xa7-mediated disease resistance was related to the biosynthesis of lignin and thus enhanced resistance to Xoo. Overall, our results provided novel insights and important resources for further clarifying the molecular mechanisms of the executor R genes.

Conjugation-Broken Dimer Acceptors Enable High-Efficiency, Stable, and Flexibility-Robust Organic Solar Cells.

Dimer acceptors in organic solar cells (OSCs) offer distinct advantages, including a well-defined molecular structure and excellent batch-to-batch reproducibility. Their high glass transition temperature (Tg) aids in achieving an optimal kinetic morphology, thereby enhancing device stability. Currently, most of dimer acceptor materials are linked with conjugated units in order to obtain high power conversion efficiencies (PCEs). In this study, different from previous works on conjugation-linked dimer acceptors, a novel series of dimer acceptors are synthesized (named T1, T4, T6, and T12), each linked with different flexible alkyl linkers, and investigated their PCEs, device stability, and flexibility robustness. When blended with PM6, the T6-based device achieves a PCE of 17.09%, comparable to the fully conjugated T0-based device's PCE of 17.12%. The molecular dynamics simulations and density functional theory calculations suggested that flexible conjugation-broken linkers (FCBLs) promote intermolecular electronic couplings, thereby maintaining good electron mobilities of dimer acceptors. Notably, the T6-based device exhibits impressive long-term stability with a T80 lifetime of 1427 h, while in the T0-based device, T80 is only 350 h. The present work has thus established the relationship between the length of flexible alkyl linkers in such dimer acceptors and the performance and stability of OSCs, which is important to further designing new materials for the fabrication of efficient and stable OSCs.

On the role of asymmetric molecular geometry in high-performance organic solar cells.

Although asymmetric molecular design has been widely demonstrated effective for organic photovoltaics (OPVs), the correlation between asymmetric molecular geometry and their optoelectronic properties is still unclear. To access this issue, we have designed and synthesized several symmetric-asymmetric non-fullerene acceptors (NFAs) pairs with identical physical and optoelectronic properties. Interestingly, we found that the asymmetric NFAs universally exhibited increased open-circuit voltage compared to their symmetric counterparts, due to the reduced non-radiative charge recombination. From our molecular-dynamic simulations, the asymmetric NFA naturally exhibits more diverse molecular interaction patterns at the donor (D):acceptor (A) interface as compared to the symmetric ones, as well as higher D:A interfacial charge-transfer state energy. Moreover, it is observed that the asymmetric structure can effectively suppress triplet state formation. These advantages enable a best efficiency of 18.80%, which is one of the champion results among binary OPVs. Therefore, this work unambiguously demonstrates the unique advantage of asymmetric molecular geometry, unveils the underlying mechanism, and highlights the manipulation of D:A interface as an important consideration for future molecular design.

Deuteration-enhanced neutron contrasts to probe amorphous domain sizes in organic photovoltaic bulk heterojunction films.

An organic photovoltaic bulk heterojunction comprises of a mixture of donor and acceptor materials, forming a semi-crystalline thin film with both crystalline and amorphous domains. Domain sizes critically impact the device performance; however, conventional X-ray scattering techniques cannot detect the contrast between donor and acceptor materials within the amorphous intermixing regions. In this study, we employ neutron scattering and targeted deuteration of acceptor materials to enhance the scattering contrast by nearly one order of magnitude. Remarkably, the PM6:deuterated Y6 system reveals a new length scale, indicating short-range aggregation of Y6 molecules in the amorphous intermixing regions. All-atom molecular dynamics simulations confirm that this short-range aggregation is an inherent morphological advantage of Y6 which effectively assists charge extraction and suppresses charge recombination as shown by capacitance spectroscopy. Our findings uncover the amorphous nanomorphology of organic photovoltaic thin films, providing crucial insights into the morphology-driven device performance.

Enhancing the organic solvent resistance of ω-amine transaminase for enantioselective synthesis of (R)-(+)-1(1-naphthyl)-ethylamine.

BACKGROUND: Biocatalysis in high-concentration organic solvents has been applied to produce various industrial products with many advantages. However, using enzymes in organic solvents often suffers from inactivation or decreased catalytic activity and stability. An R-selective ω-amine transaminase from Aspergillus terreus (AtATA) exhibited activity toward 1-acetylnaphthalene. However, AtATA displayed unsatisfactory organic solvent resistance, which is required to enhance the solubility of the hydrophobic substrate 1-acetylnaphthalene. So, improving the tolerance of enzymes in organic solvents is essential. MAIN METHODS AND RESULTS: The method of regional random mutation combined with combinatorial mutation was used to improve the resistance of AtATA in organic solvents. Enzyme surface areas are structural elements that undergo reversible conformational transitions, thus affecting the stability of the enzyme in organic solvents. Herein, three surface areas containing three loops were selected as potential mutation regions. And the "best" mutant T23I/T200K/P260S (M3) was acquired. In different concentrations of dimethyl sulfoxide (DMSO), the catalytic efficiency (kcat /Km ) toward 1-acetylnaphthalene and the stability (half-life t1/2 ) were higher than the wild-type (WT) of AtATA. The results of decreased Root Mean Square Fluctuation (RMSF) values via 20-ns molecular dynamics (MD) simulations under 15%, 25%, 35%, and 45% DMSO revealed that mutant M3 had lower flexibility, acquiring a more stable protein structure and contributing to its organic solvents stability than WT. Furthermore, M3 was applied to convert 1-acetylnaphthalene for synthesizing (R)-(+)-1(1-naphthyl)-ethylamine ((R)-NEA), which was an intermediate of Cinacalcet Hydrochloride for the treatment of secondary hyperthyroidism and hypercalcemia. Moreover, in a 20-mL scale-up experiment, 10 mM 1-acetylnaphthalene can be converted to (R)-NEA with 85.2% yield and a strict R-stereoselectivity (enantiomeric excess (e.e.) value >99.5%) within 10 h under 25% DMSO. CONCLUSION: The beneficial mutation sites were identified to tailor AtATA's organic solvents stability via regional random mutation. The "best" mutant T23I/T200K/P260S (M3) holds great potential application for the synthesis of (R)-NEA.

De Novo Designed Self-Assembling Rhodamine Probe for Real-Time, Long-Term and Quantitative Live-Cell Nanoscopy.

Super-resolution imaging provides a powerful approach to image dynamic biomolecule events at nanoscale resolution. An ingenious method involving tuning intramolecular spirocyclization in rhodamine offers an appealing strategy to design cell-permeable fluorogenic probes for super-resolution imaging. Nevertheless, precise control of rhodamine spirocyclization presents a significant challenge. Through detailed study of the structure-activity relationship, we identified that multiple key factors control rhodamime spirocyclization. The findings provide opportunities to create fluorogenic probes with tailored properties. On the basis of our findings, we constructed self-assembling rhodamine probes for no-wash live-cell confocal and super-resolution imaging. The designed self-assembling probe Rho-2CF3 specifically labeled its target proteins and displayed high ring-opening ability, fast labeling kinetics (<1 min), and large turn-on fold (>80 folds), which is very difficult to be realized by the existing methods. Using the probe, we achieved high-contrast super-resolution imaging of nuclei and mitochondria with a spatial resolution of up to 42 nm. The probe also showed excellent photostability and proved ideal for real-time and long-term tracking of mitochondrial fission and fusion events with high spatiotemporal resolution. Furthermore, Rho-2CF3 could resolve the ultrastructure of mitochondrial cristae and quantify their morphological changes under drug treatment at nanoscale. Our strategy thus demonstrates its usefulness in designing self-assembling probes for super-resolution imaging.

Rapid and Directional Improvement of Elite Rice Variety via Combination of Genomics and Multiplex Genome Editing.

High yield and superior quality are the main goals pursued by breeders for crop improvement. However, both of them are complex agronomic traits controlled by multiple genes, so the simultaneous improvement of these traits via sexual recombination is time-consuming and direction-uncontrolled. In this study, to solve this dilemma, we introduced the comparative genomic analysis based multiplex genome editing system (CG-MGE), a method for rapid and directional improvement of multiple traits. Application of this method, association analysis between genotypes and phenotypes was carried out to mine excellent alleles; subsequently, the rare excellent alleles of Gn1a, GW2, TGW3, and Chalk5 were simultaneously created by multiplex genome editing and successfully improved the plant architecture, grain yield, and quality of a widely cultivated elite rice variety. Overall, this study provides a method for rapid and directional improvement of crops, and the application of the CG-MGE will be helpful to accelerate rational design breeding.

Knockout of a papain-like cysteine protease gene OCP enhances blast resistance in rice.

Papain-like cysteine proteases (PLCPs) play an important role in the immune response of plants. In Arabidopsis, several homologous genes are known to be involved in defending against pathogens. However, the effects of PLCPs on diseases that afflict rice are largely unknown. In this study, we show that a PLCP, an oryzain alpha chain precursor (OCP), the ortholog of the Arabidopsis protease RD21 (responsive to dehydration 21), participates in regulating resistance to blast disease with a shorter lesion length characterizing the knockout lines (ocp-ko), generated via CRISPR/Cas9 technology. OCP was expressed in all rice tissues and mainly located in the cytoplasm. We prove that OCP, featuring cysteine protease activity, interacts with OsRACK1A (receptor for activated C kinase 1) and OsSNAP32 (synaptosome-associated protein of 32 kD) physically in vitro and in vivo, and they co-locate in the rice cytoplasm but cannot form a ternary complex. Many genes related to plant immunity were enriched in the ocp-ko1 line whose expression levels changed significantly. The expression of jasmonic acid (JA) and ethylene (ET) biosynthesis and regulatory genes were up-regulated, while that of auxin efflux transporters was down-regulated in ocp-ko1. Therefore, OCP negatively regulates blast resistance in rice by interacting with OsRACK1A or OsSNAP32 and influencing the expression profiles of many resistance-related genes. Moreover, OCP might be the cornerstone of blast resistance by suppressing the activation of JA and ET signaling pathways as well as promoting auxin signaling pathways. Our research provides a comprehensive resource of PLCPs for rice plants in defense against pathogens that is also of potential breeding value.

Microstructure and Corrosion Resistance of Underwater Laser Cladded Duplex Stainless Steel Coating after Underwater Laser Remelting Processing.

Combined with the technologies of underwater local dry laser cladding (ULDLC) and underwater local dry laser remelting (ULDLR), a duplex stainless steel (DSS) coating has been made in an underwater environment. The phase composition, microstructure, chemical components and electrochemical corrosion resistance was studied. The results show that after underwater laser remelting, the phase composition of DSS coating remains unchanged and the phase transformation from Widmanstätten austenite + intragranular austenite + (211) ferrite to (110) ferrite occurred. The ULDLR process can improve the corrosion resistance of the underwater local dry laser cladded coating. The corrosion resistance of remelted coating at 3 kW is the best, the corrosion resistance of remelted coating at 1kW and 5kW is similar and the corrosion resistance of (110) ferrite phase is better than grain boundary austenite phase. The ULDLC + ULDLR process can meet the requirements of efficient underwater maintenance, forming quality control and corrosion resistance. It can also be used to repair the surface of S32101 duplex stainless steel in underwater environment.

Improving the Thermostability and Activity of Transaminase From Aspergillus terreus by Charge-Charge Interaction.

Transaminases that promote the amination of ketones into amines are an emerging class of biocatalysts for preparing a series of drugs and their intermediates. One of the main limitations of (R)-selective amine transaminase from Aspergillus terreus (At-ATA) is its weak thermostability, with a half-life (t 1/2) of only 6.9 min at 40°C. To improve its thermostability, four important residue sites (E133, D224, E253, and E262) located on the surface of At-ATA were identified using the enzyme thermal stability system (ETSS). Subsequently, 13 mutants (E133A, E133H, E133K, E133R, E133Q, D224A, D224H, D224K, D224R, E253A, E253H, E253K, and E262A) were constructed by site-directed mutagenesis according to the principle of turning the residues into opposite charged ones. Among them, three substitutions, E133Q, D224K, and E253A, displayed higher thermal stability than the wild-type enzyme. Molecular dynamics simulations indicated that these three mutations limited the random vibration amplitude in the two α-helix regions of 130-135 and 148-158, thereby increasing the rigidity of the protein. Compared to the wild-type, the best mutant, D224K, showed improved thermostability with a 4.23-fold increase in t 1/2 at 40°C, and 6.08°C increase in T 50 10 . Exploring the three-dimensional structure of D224K at the atomic level, three strong hydrogen bonds were added to form a special "claw structure" of the α-helix 8, and the residues located at 151-156 also stabilized the α-helix 9 by interacting with each other alternately.