Synthesis of molecularly imprinted polymers for amino acid derivates by using different functional monomers

Fmoc-3-nitrotyrosine (Fmoc-3-NT) molecularly imprinted polymers (MIPs) were synthesized to understand the influence of several functional monomers on the efficiency of the molecular imprinting process. Acidic, neutral and basic functional monomers, such as acrylic acid (AA), methacrylic acid (MAA), methacrylamide (MAM), 2-vinylpyridine (2-VP), 4-vinylpyridine (4-VP), have been used to synthesize five different polymers. In this study, the MIPs were tested in batch experiments by UV-visible spectroscopy in order to evaluate their binding properties. The MIP prepared with 2-VP exhibited the highest binding affinity for Fmoc-3NT, for which Scatchard analysis the highest association constant (2.49 × 10⁴ M⁻¹) was obtained. Furthermore, titration experiments of Fmoc-3NT into acetonitrile solutions of 2-VP revealed a stronger bond to the template, such that a total interaction is observed. Non-imprinted polymers as control were prepared and showed no binding affinities for Fmoc-3NT. The results are indicative of the importance of ionic bonds formed between the –OH residues of the template molecule and the pyridinyl groups of the polymer matrix. In conclusion, 2-VP assists to create a cavity which allows better access to the analytes.

Production and Directional Evolution of Antisarafloxacin ScFv Antibody for Immunoassay of Fluoroquinolones in Milk

A recombinant antisarafloxacin ScFv antibody was produced by direct transformation of its gene into Rosetta-gami(DE3) for expression, and then its recognition mechanisms for 12 fluoroquinolones were studied using the molecular docking method. On the basis of the results of virtual mutation, the ScFv antibody was evolved by directional mutagenesis of contact amino acid residue Tyr99 to His. The ScFv mutant showed highly increased affinity for the 12 drugs with up to sevenfold improved sensitivity. Finally, the mutant was used to develop an indirect competitive enzyme linked immunosorbent assay for determination of the 12 drugs in milk. The limits of detection were in the range of 0.3-8.0 ng/mL; the ties were in the range of 5-106%, and the recoveries from the standard fortified blank milk were in the range of 62.0-89.3%. This is the first study reporting the evolution of an ScFv antibody using a directional mutagenesis strategy based on virtual mutation.

Homochiral Zeolitic Imidazolate Framework with Defined Chiral Microenvironment for Electrochemical Enantioselective Recognition

The recognition and separation of chiral molecules with similar structure are of great industrial and biological importance. Development of highly efficient chiral recognition systems is crucial for the precise application of these chiral molecules. Herein, a homochiral zeolitic imidazolate frameworks (c-ZIF) functionalized nanochannel device that exhibits an ideal platform for electrochemical enantioselective recognition is reported. Its distinct chiral binding cavity enables more sensitive discrimination of tryptophan (Trp) enantiomer pairs than other smaller chiral amino acids owing to its size matching to the target molecule. It is found that introducing neighboring aldehyde groups into the chiral cavity will result in an inferior chiral Trp recognition due to the decreased adsorption-energy difference of D- and L-Trp on the chiral sites. This study may provide an alternative strategy for designing efficient chiral recognition devices by utilizing the homochiral reticular materials and tailoring their chiral environments.

Preparation and Directed Evolution of Anti-Ciprofloxacin ScFv for Immunoassay in Animal-Derived Food

An immunized mouse phage display scFv library with a capacity of 3.34 × 10⁹ CFU/mL was constructed and used for screening of recombinant anti-ciprofloxacin single-chain antibody for the detection of ciprofloxacin (CIP) in animal-derived food. After four rounds of bio-panning, 25 positives were isolated and identified successfully. The highest positive scFv-22 was expressed in E. coli BL21. Then, its recognition mechanisms were studied using the molecular docking method. The result showed the amino acid residue Val160 was the key residue for the binding of scFv to CIP. Based on the results of virtual mutation, the scFv antibody was evolved by directional mutagenesis of contact amino acid residue Val160 to Ser. After the expression and purification, an indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) based on the parental and mutant scFv was established for CIP, respectively. The IC50 value of the assay established with the ScFv mutant was 1.58 ng/mL, while the parental scFv was 26.23 ng/mL; this result showed highly increased affinity, with up to 16.6-fold improved sensitivity. The mean recovery for CIP ranged from 73.80% to 123.35%, with 10.46% relative standard deviation between the intra-assay and the inter-assay. The RSD values ranged between 1.49% and 9.81%. The results indicate that we obtained a highly sensitive anti-CIP scFv by the phage library construction and directional evolution, and the scFv-based IC-ELISA is suitable for the detection of CIP residue in animal-derived edible tissues.

Conformational studies of RGDechi peptide by natural-abundance NMR spectroscopy

Integrins are heterodimeric cell-surface proteins that play important roles during developmental and pathological processes. Diverse human pathologies involve integrin adhesion including thrombotic diseases, inflammation, tumour progression, fibrosis, and infectious diseases. Although in the past decade, novel integrin-inhibitor drugs have been developed for integrin-based medical applications, the structural determinants modulating integrin-ligands recognition mechanisms are still poorly understood, reducing the number of integrin subtype exclusive antagonists. In this scenario, we have very recently showed, by means of chemical and biological assays, that a chimeric peptide (named RGDechi), containing a cyclic RGD motif linked to an echistatin C-terminal fragment, is able to interact with the components of integrin family with variable affinities, the highest for α_v β3. Here, in order to understand the mechanistic details driving the molecular recognition mechanism of α_v β₃ by RGDechi, we have performed a detailed structural and dynamics characterization of the free peptide by natural abundance nuclear magnetic resonance (NMR) spectroscopy. Our data indicate that RGDechi presents in solution an heterogeneous conformational ensemble characterized by a more constrained and rigid pentacyclic ring and a largely unstructured acyclic region. Moreover, we propose that the molecular recognition of α_v β₃ integrin by RGDechi occurs by a combination of conformational selection and induced fit mechanisms. Finally, our study indicates that a detailed NMR characterization, by means of natural abundance ¹⁵ N and ¹³ C, of a mostly unstructured bioactive peptide may provide the molecular basis to get essential structural insights into the binding mechanism to the biological partner.

Recognition and Selectivity Analysis Monitoring of Multicomponent Steroid Estrogen Mixtures in Complex Systems Using a Group-Targeting Environmental Sensor

The same class of steroid estrogen mixtures, coexisting in the environment of 17β-estradiol, estrone (E1), and ethinyl estradiol (EE2), have strong ability to disrupt the human endocrine system and are seriously prejudicial to the health of the organism and environmental safety. Herein, a highly sensitive and group-targeting environmental monitoring sensor was fabricated for a comprehensive analysis of multicomponent steroid estrogens (multi-SEs) in complex systems. This breakthrough was based on the highly sensitive photoelectrochemical response composite material CdSe NPs-TiO₂ nanotube and highly group-specific aptamers. The optimized procedure exhibited not only high sensitivity in a wide range of concentrations from 0.1 to 50 nM, indeed, the minimum detection limit was 33 pM, but also strong resistance to interference. The affinity and consistent action pockets of this sensor enable selective detection of multi-SEs in complex systems. It subsequently was applied for the analysis of multi-SEs from three real samples in the environment including medical wastewater, river water, and tap water to provide a means to clarify the fate of multi-SEs in the process of migration and transformation. This monitoring sensor has a brilliant application prospect for the identification and monitoring of the same class of endocrine-disrupting chemical mixtures in environmental complex systems.

Molecular Recognition Mechanism of an Anti-Amatoxins mAb and Its Application in Centrifugal Disk-Based Immunoassay

Amatoxins are polypeptides that cause 90% of fatalities from accidental ingestion of poisonous mushrooms. Unfortunately, there are no specific antidotes against amatoxins poisoning, hence preparation of high-affinity antibodies, understanding the receptor (amatoxins) and ligand (antibody) mechanism, and establishing a straightforward screening approach are of great significance for confirming poison agents and clinical diagnosis. Here, anti-amatoxins monoclonal antibody (mAb) 9B2 was prepared and the recognition mechanism was investigated. The approach is useful for designing desirable immunogens, developing new antibodies with improved performance, and constructing effective immunoassays. Based on the mAb, we designed a centrifugal disk-like microfluidics chip and developed a fully automated immunoassay capable of detecting amatoxins poisoning in various samples including serum, urine, and mushrooms. The whole detection process could be automatically accomplished within 30 min, with a limit of detection of 0.08 to 0.12 μg/L for real samples, ∼30-fold more sensitive than conventional enzyme-linked immunosorbent assay (ELISA). Our platform not only provided a practical approach for performing poison agent confirmation and clinical diagnosis but also had important implications for improving the survival of patients with mushroom poisoning.

Development of a Dihydropteroate Synthase-Based Fluorescence Polarization Assay for Detection of Sulfonamides and Studying Its Recognition Mechanism

In this study, the dihydropteroate synthase of Staphylococcus aureus was obtained, and its recognition mechanisms for 31 sulfonamide drugs were studied. Results showed that their core structure matched well with the binding pocket of para-aminobenzoic acid, and all the sulfonamide side chains were out of the binding pocket. Hydrogen bonds and hydrophobic interactions were the main intermolecular forces, and the key amino acids were Gly171 and Lys203. The binding sites in sulfonamide molecules were mainly around the para-aminobenzenesulfonamide part. This enzyme was used to develop a fluorescence polarization assay for detection of these drugs in chicken muscles. The change trends of half of inhibition concentrations and cross-reactivities for the 31 drugs were identical with the receptor-ligand affinities. The limits of detection were in the range of 2.0-38.5 ng/g, and one assay could be finished within several minutes. Therefore, this method could be used for multiscreening of sulfonamide residues in meat samples.

Structural insight into chitin perception by chitin elicitor receptor kinase 1 of Oryza sativa

Plants have developed innate immune systems to fight against pathogenic fungi by monitoring pathogenic signals known as pathogen-associated molecular patterns (PAMP) and have established endo symbiosis with arbuscular mycorrhizal (AM) fungi through recognition of mycorrhizal (Myc) factors. Chitin elicitor receptor kinase 1 of Oryza sativa subsp. Japonica (OsCERK1) plays a bifunctional role in mediating both chitin-triggered immunity and symbiotic relationships with AM fungi. However, it remains unclear whether OsCERK1 can directly recognize chitin molecules. In this study, we show that OsCERK1 binds to the chitin hexamer ((NAG)₆ ) and tetramer ((NAG)₄ ) directly and determine the crystal structure of the OsCERK1-(NAG)₆ complex at 2 Å. The structure shows that one OsCERK1 is associated with one (NAG)₆ . Upon recognition, chitin hexamer binds OsCERK1 by interacting with the shallow groove on the surface of LysM2. These structural findings, complemented by mutational analyses, demonstrate that LysM2 is crucial for recognition of both (NAG)₆ and (NAG)₄ . Altogether, these findings provide structural insights into the ability of OsCERK1 in chitin perception, which will lead to a better understanding of the role of OsCERK1 in mediating both immunity and symbiosis in rice.

Investigation of Taniaphos as a chiral selector in chiral extraction of amino acid enantiomers

Finding chiral selector with high stereoselectivity to a variety of amino acid enantiomers remains a challenge and warrants further research. In this work, Taniaphos, a chiral ligand with rotatable spatial configuration, was employed as a chiral extractant to enantioseparate various amino acid enantiomers. Phenylalanine (Phe), homophenylalanine (Hphe), 4-nitrophenylalanine (Nphe), and 3-chloro-phenylglycine (Cpheg) were used as substrates to evaluate the extraction efficiency. The results revealed that Taniaphos-Cu exhibited good abilities to enantioseparate Phe, Hphe, Nphe, and Cpheg with the highest separation factors (α) of 3.13, 2.10, 2.32, and 2.14, respectively. Taniaphos-Cu is more conducive to combine with D-amino acid in extraction. The influences of pH, Taniaphos-Cu, and concentration and extraction temperature on extraction were comprehensively evaluated. The highest performance factors (pf) for Phe, Hphe, Nphe, and Cpheg at optimal extraction conditions were 0.08892, 0.1250, 0.09621, and 0.08021, respectively. The recognition mechanism between Taniaphos-Cu and amino acid enantiomers was discussed. The coordination interaction between Taniaphos-Cu and COO- , π-π interaction between Taniaphos-Cu and amino acid enantiomers are important acting forces in chiral extraction. The steric-hindrance between NH2 and OH lead to Taniaphos-Cu-D-Phe is more stable than Taniaphos-Cu-L-Phe. This work provided a chiral extractant that has good abilities to enantioseparate various amino acid enantiomers.

Development of a Progesterone-Receptor-Based Pseudo-immunoassay for Multi-detection of Progestins in Milk and Studying Its Recognition Mechanism

The residues of progestins in milk are dangerous to consumers, but an immunoassay capable of multi-determining progestins in milk has not been reported thus far. In this study, the ligand binding domain of the human progesterone receptor was expressed and its intermolecular interactions with the commonly used steroid hormones were studied. The docking results showed that the receptor fragment only recognized progestins and did not recognize other steroid hormones. Then, it was used as recognition material to develop a pseudo-direct competitive enzyme-linked immunosorbent assay for multi-determination of five progestins in milk. Because biotinylated horseradish peroxidase was combined with streptavidinated horseradish peroxidase to enhance the signal, the sensitivities for the five progestins (IC50 of 0.029-0.097 ng/mL) were improved 96-143-fold in comparison to the use of the conventional horseradish peroxidase signal system (IC50 of 3.0-12.5 ng/mL). This method showed negligible cross-reactivities to other steroid hormones, consistent with the docking results. This was the first paper developing a progesterone-receptor-based method for detection of progestins, and this method exhibited generally better performance than all of the previously reported immunoassays for progestins.

The Activating receptor KIR2DS2 bound to HLA-C1 reveals the novel recognition features of activating receptor

Killer cell immunoglobulin-like receptors (KIRs) are important receptors for regulating the killing of virus-infected or cancer cells of natural killer (NK) cells. KIR2DS2 can recognize peptides derived from hepatitis C virus (HCV) or global flaviviruses (such as dengue and Zika) presented by HLA-C*0102 to activate NK cells, and have shown promising results when used for cancer immunotherapy. Here, we present the complex structure of KIR2DS2 with HLA-C*0102 at a resolution of 2.5Å. Our structure reveals that KIR2DS2 can bind HLA-C*0102 and HLA-A*1101 in two different directions. Moreover, Tyr45 (in activating receptor KIR2DS2) and Phe45 (in inhibitory KIRs) distinguish the two different binding models and binding affinity between activating KIRs and inhibitory KIRs. The conserved "AT" motif of the peptide mediates recognition and determines the peptide specificity of recognition. These structural characteristic shed light on how KIRs activate NK cells and can provide a molecular basis for immunotherapy by NK cells.

Combined prediction and design reveals the target recognition mechanism of an intrinsically disordered protein interaction domain

An increasing number of protein interaction domains and their targets are being found to be intrinsically disordered proteins (IDPs). The corresponding target recognition mechanisms are mostly elusive because of challenges in performing detailed structural analysis of highly dynamic IDP-IDP complexes. Here, we show that by combining recently developed computational approaches with experiments, the structure of the complex between the intrinsically disordered C-terminal domain (CTD) of protein 4.1G and its target IDP region in NuMA can be dissected at high resolution. First, we carry out systematic mutational scanning using dihydrofolate reductase-based protein complementarity analysis to identify essential interaction regions and key residues. The results are found to be highly consistent with an α/β-type complex structure predicted by AlphaFold2 (AF2). We then design mutants based on the predicted structure using a deep learning protein sequence design method. The solved crystal structure of one mutant presents the same core structure as predicted by AF2. Further computational prediction and experimental assessment indicate that the well-defined core structure is conserved across complexes of 4.1G CTD with other potential targets. Thus, we reveal that an intrinsically disordered protein interaction domain uses an α/β-type structure module formed through synergistic folding to recognize broad IDP targets. Moreover, we show that computational prediction and experiment can be jointly applied to segregate true IDP regions from the core structural domains of IDP-IDP complexes and to uncover the structure-dependent mechanisms of some otherwise elusive IDP-IDP interactions.

Recent Progress in Diboronic-Acid-Based Glucose Sensors

Non-enzymatic sensors with the capability of long-term stability and low cost are promising in glucose monitoring applications. Boronic acid (BA) derivatives offer a reversible and covalent binding mechanism for glucose recognition, which enables continuous glucose monitoring and responsive insulin release. To improve selectivity to glucose, a diboronic acid (DBA) structure design has been explored and has become a hot research topic for real-time glucose sensing in recent decades. This paper reviews the glucose recognition mechanism of boronic acids and discusses different glucose sensing strategies based on DBA-derivatives-based sensors reported in the past 10 years. The tunable pK_a, electron-withdrawing properties, and modifiable group of phenylboronic acids were explored to develop various sensing strategies, including optical, electrochemical, and other methods. However, compared to the numerous monoboronic acid molecules and methods developed for glucose monitoring, the diversity of DBA molecules and applied sensing strategies remains limited. The challenges and opportunities are also highlighted for the future of glucose sensing strategies, which need to consider practicability, advanced medical equipment fitment, patient compliance, as well as better selectivity and tolerance to interferences.

Specific Recognition of the 5'-Untranslated Region of West Nile Virus Genome by Human Innate Immune System

In the last few years, the sudden outbreak of COVID-19 caused by SARS-CoV-2 proved the crucial importance of understanding how emerging viruses work and proliferate, in order to avoid the repetition of such a dramatic sanitary situation with unprecedented social and economic costs. West Nile Virus is a mosquito-borne pathogen that can spread to humans and induce severe neurological problems. This RNA virus caused recent remarkable outbreaks, notably in Europe, highlighting the need to investigate the molecular mechanisms of its infection process in order to design and propose efficient antivirals. Here, we resort to all-atom Molecular Dynamics simulations to characterize the structure of the 5′-untranslated region of the West Nile Virus genome and its specific recognition by the human innate immune system via oligoadenylate synthetase. Our simulations allowed us to map the interaction network between the viral RNA and the host protein, which drives its specific recognition and triggers the host immune response. These results may provide fundamental knowledge that can assist further antivirals’ design, including therapeutic RNA strategies.

[Preparation of chiral metal organic framework modified silica monolithic capillary column and its application in enantioseparations of chiral drugs]

Metal organic frameworks (MOFs) are crystalline compounds composed of metal ions (or metal clusters) and organic ligands. Chiral MOFs have been successfully utilized as novel materials for the separation of chiral enantiomers by chromatography, demonstrating excellent chiral separation performance. In this study, a chiral MOF-modified silica monolithic capillary column was used for pressurized capillary electrochromatography. First, a chiral MOF (Co-glycyl-L-glutamic acid, Co-L-GG) was synthesized. This MOF was then used to prepare a chiral capillary monolithic column via a one-step in situ polymerization method. The optimal conditions for preparing the chiral capillary monolithic column were determined as follows: Co-L-GG amount, 5 mg; polyethylene glycol amount, 0.96 mg; tetramethoxysilane dosage, 3.6 mL; trimethoxymethylsilane dosage, 0.4 mL. Next, the effects of the separation conditions on the separation of chiral drugs were investigated. Under the conditions of an applied voltage of -20 kV and a mobile phase consisting of acetonitrile and 20 mmol/L disodium hydrogen phosphate (80∶20, v/v), six chiral drugs were separated within 3 min, with baseline separation achieved for amlodipine, fluvastatin, and tryptophan. Moreover, the prepared chiral capillary monolithic column exhibited good reproducibility and stability. Finally, molecular docking studies were conducted using AutoDock to explore the chiral recognition mechanism, and the results were analyzed using Discovery Studio. The results indicated that larger differences in binding free energy between Co-L-GG and the enantiomers of the chiral drugs were correlated with higher enantioselectivity factors. However, this correlation did not necessarily lead to an increase in resolution. Co-L-GG, which is enriched with primary amines, secondary amines, and carbonyl groups, demonstrated enantiomeric recognition capability. In conclusion, this study demonstrates that chiral MOFs can be effectively used as chiral functional monomers to prepare chiral monolithic capillary columns, highlighting their significant potential for the separation and analysis of chiral compounds. The comprehensive exploration of the synthesis, characterization, and applications of these MOFs will help provide valuable insights into the development of advanced separation technologies.

Preparation of amino acid chiral ionic liquid and visual chiral recognition of glutamine and phenylalanine enantiomers

In this paper, the amino acid chiral ionic liquid (AACIL) was prepared with L-phenylalanine and imidazole. It was characterized by CD, FT-IR, 1H NMR, and 13C NMR spectrum. The chiral recognition sensor was constructed with AACIL and Cu(II), which exhibited different chiral visual responses (solubility or color difference) to the enantiomers of glutamine (Gln) and phenylalanine (Phe). The effects of solvent, pH, time, temperature, metal ions, and other amino acids on visual chiral recognition were optimized. The minimum concentrations of Gln and Phe for visual chiral recognition were 0.20 mg/ml and 0.28 mg/ml, respectively. The mechanism of chiral recognition was investigated by FT-IR, TEM, SEM, TG, XPS, and CD. The location of the host-guest inclusion or molecular placement has been conformationally searched based on Gaussian 09 software.

Cuckoo Hosts Fine-Tune Their Egg Rejection After Experiencing a Parasitism Event

Recognising and rejecting parasitic eggs is one of the most common anti-parasitism strategies used by host birds. However, the egg rejection of some hosts exhibits behavioural plasticity. To investigate whether the egg rejection behaviour of host birds changes after encountering a parasitism event, we conducted egg rejection experiments on the locally most common host of the common cuckoo (Cuculus canorus), the grey bushchat (Saxicola ferreus) in Yunnan, China. When a single pure white egg of the white-rumped munia (Lonchura striata) or a blue model egg was individually added to the nest of the grey bushchat, the rejection rate for the white-rumped munia eggs was as high as 93.3%, whereas the rejection rate for the blue model egg was minimal (5.56%). However, when the grey bushchat rejected the munia egg and a blue model egg was subsequently added to its nest, the rejection rate for the blue model egg was significantly higher, reaching 54.5%. When recognised, the presence of a non-mimetic foreign egg in the nest may then act as a cue indicating high parasitism risk for the host. Consequently, the bird may intensify its inspection of nest eggs, leading to increased rejection of the previously accepted blue model eggs. Our results are consistent with the optimal acceptance threshold hypothesis, suggesting that as the parasitism risk increases, the grey bushchat adjusts its acceptance threshold for foreign eggs to become more stringent.

Production of AmpC β-Lactamase and Development of a Competitive Array for Discriminative Determination of Cephalosporins in Milk

In this study, AmpC β-lactamase of Escherichia coli was expressed, and its intermolecular interaction mechanisms with 15 cephalosporins (CPs) were studied by using a molecular docking technique. Results showed that this enzyme mainly interacted with the β-lactam ring of these CPs, and the key contacting amino acids were Ser80 and Ser228. The AmpC β-lactamase was combined with 5 horseradish peroxidase-labeled conjugates to develop a direct competitive array on a microplate for determination of 15 drugs in milk. Due to the use of principal component analysis method to analyze the data, this method could discriminate the 15 drugs at the concentration as low as 10 ng/mL. The detection results for the unknown milk samples were consistent with those obtained by the liquid chromatography-mass spectrometry method. As a general comparison, this method is better than the previous antibody-based and receptor-based detection methods for CPs. This is the first paper reporting a competitive array for discriminative determination of a class of small-molecule substances.

Study of the Enantioselectivity and Recognition Mechanism of Allyl-β-CD Modified Organic Polymer Monolithic Capillary Column

Allyl-β-CD was synthesized and used as the chiral functional monomer to prepare chiral organic polymer monolithic columns in capillary HPLC. First, the enantioselectivity of the prepared allyl-β-CD modified organic polymer monolithic capillary columns was investigated. Then, the influences of enantioseparation conditions of chiral drugs were further explored. Finally, the recognition mechanism was studied by molecular docking with AutoDock. Complete enantioseparations of four chiral drugs as well as partial enantioseparations of eight chiral drugs have been achieved. Results showed that the RSD values for run-to-run, day-to-day, and column-to-column variations ranged from 1.2% to 4.6%, 1.4% to 4.7%, and 2.0% to 6.1%, respectively. The enantioselectivity factor rather than resolution is correlated with the binding free energy difference between enantiomers with allyl-β-CD. Furthermore, the abundant ether bonds, hydroxyl groups, and hydrophobic cavities in cyclodextrin are responsible for the enantioseparation ability of the chiral monolithic capillary columns.

Central Chirality and Axial Chirality Recognition of the Enantioselective Antibodies to Herbicide Metolachlor

Enantioselective antibodies have emerged as efficient tools in the field of chiral chemical detection and separation. However, it is complicated to obtain a highly stereoselective antibody due to the unclear recognition mechanism. In this study, the hapten of metolachlor was synthesized and enantio-separated. The absolute configuration of the four haptens obtained was identified by the computed and experimental electronic circular dichroism comparison. Five polyclonal antibodies against the Rac-metolachlor and its enantiomers were generated by immunization. The cross-activity of all the 5 antibodies with 44 structural analogues, including metolachlor enantiomers, was tested. It demonstrated that antibodies have higher specificity to recognize central chirality than axial chirality. Especially, αRR-MET-Ab exhibited excellent specificity and stereoselectivity. Accordingly, 3D-QSAR models were constructed and revealed that paired stereoisomers exhibited opposite interactions with the antibodies. It is the first time that the antibodies against four stereoisomers were prepared and analyzed, which will be conducive to the rational design of the stereoselective antibodies.

Identification and Evolution of a Natural Tetr Protein Based on Molecular Docking and Development of a Fluorescence Polari-Zation Assay for Multi-Detection of 10 Tetracyclines in Milk

In this study, the identity of our recently produced natural TetR protein was identified by using the LC-ESI-MS/MS technique, and its recognition mechanisms, including the binding pocket, contact amino acids, intermolecular forces, binding sites, binding energies, and affinities for 10 tetracycline drugs were studied. Then, it was evolved by site-mutagenesis of an amino acid to produce a mutant, and a fluorescence polarization assay was developed to detect the 10 drugs in milk. The sensitivities for the 10 drugs were improved with IC₅₀ values decreasing from 30.8-80.1 ng/mL to 15.5-55.2 ng/mL, and the limits of detection were in the range of 0.4-1.5 ng/mL. Furthermore, it was found that the binding affinity for a drug was the critical factor determining its sensitivity, and the binding energy showed little influence. This is the first study reporting the recognition mechanisms of a natural TetR protein for tetracyclines and the development of a fluorescence polarization assay for the detection of tetracyclines residues in food samples.

Recombinant Antibody-Based and Computer-Aided Comprehensive Analysis of Antibody's Equivalent Recognition Mechanism of Alternariol and Alternariol Monomethyl Ether

Alternariol (AOH) and alternariol monomethyl ether (AME) are two main Alternaria mycotoxins that endanger human health. In this study, a single-chain antibody fragment (scFv) capable of equivalently and specifically recognizing AOH and AME was first expressed, and its equivalent recognition mechanism was discussed. According to molecular docking and dynamic simulation, the C9 site, which was always exposed outside the binding cavity, made the structural differences between AOH and AME negligible. Due to the high similarity of structures, AOH and AME interacted with almost the same amino acids on the scFv; thus, the same interaction mode and interaction force were produced. This was considered to be the most critical reason for the equivalent recognition. Thus, the exposure of common structures was considered a potential strategy to obtain the equivalent recognition antibodies, and C9 was considered the key site in the process of hapten modification. These results laid a theoretical foundation for further research on antibodies against Alternaria mycotoxins. It could promote the rapid detection of AOH and AME in food and provide a new idea for targeted preparation of antibodies that could recognize multiple hazards with similar structures.

The fluorescence of a mercury probe based on osthol

The ability of osthol (OST) to recognize mercury ions in aqueous solution was studied using fluorescence, UV–vis spectrophotometry, mass spectrometry, and ¹H NMR spectroscopy, and the recognition mechanism is discussed. The results showed that OST and Hg²⁺ can form a complex with a stoichiometric ratio of 1:1. The binding constant was 1.552 × 10⁵ L∙mol⁻¹, having a highly efficient and specific selectivity for Hg²⁺. The fluorescence intensity of OST showed a good linear correlation with the Hg²⁺ concentration (6.0 × 10⁻⁵ to 24.0 × 10⁻⁵ mol∙L⁻¹, R² = 0.9954), and the detection limit of the probe was 5.04 × 10⁻⁸ mol∙L⁻¹, which can be used for the determination of Hg²⁺ traces.