Structural Analysis of Anti-Hapten Antibodies to Identify Long-Range Structural Movements Induced by Hapten Binding

A non-classical view of antibody properties: Allosteric effect between variable and constant regions

Historically, antibodies have been divided into two functionally independent domains, the variable (V) region for antigen binding and the constant (C) region for mediating effector functions. However, this classical view of antibody function has been severely challenged by a large and growing number of studies, which reveal long-range conformational interactions and allosteric links between the V and C regions. This review comprehensively summarizes the existing studies on antibody allostery, including allosteric conformational changes induced by covalent modifications or noncovalent ligand binding. In addition, we discuss how intramolecular allosteric signals are transmitted from the V to C regions and vice versa. This review argues that there is sufficient evidence to revisit the structure-function relationship of antibodies. These advances in antibody allostery will provide a blueprint for regulating antibody functions in a simple and highly predictable manner. More focus on antibody allostery will definitely benefit antibody engineering and vaccine design in the field of biotechnology.

Application of Anti-Immune Complex Reagents in Small Molecule Analyte Immunoassays

The detection of small molecule analytes (SMAs) is of great significance for food and drug testing, environmental monitoring, and disease diagnosis. However, the performance of commercially available SMA immunoassays is limited by their low sensitivity and specificity due to the competitive format, leaving significant room for improvement. In recent years, the application of noncompetitive immunoassays for the detection of SMAs has become a hot topic, especially with the rapid evolution of antibody development technology. The remarkable development and application of anti-immune complex (anti-IC) reagents targeting antigen-specific antibodies have garnered significant interest from researchers and diagnostic companies, particularly in the field of SMA detection. The discovery and development history of anti-IC antibodies, the advantages and limitations of different anti-IC reagent preparation methods, and the mechanisms of interaction between ICs and anti-IC antibodies are reviewed. A comprehensive overview of the application of anti-IC antibodies in SMAs assay, including pesticide residue detection, mycotoxin detection, and clinical testing, as well as current challenges and potential solutions in noncompetitive immunoassays, is also summarized to provide a reference for the rapid and accurate detection of SMAs.

Drastic alterations in the loop structure around colchicine upon complex formation with an engineered lipocalin indicate a conformational selection mechanism

Using Anticalin technology, a lipocalin protein dubbed Colchicalin, with the ability to bind the toxic plant alkaloid colchicine with picomolar affinity, has previously been engineered, thus offering a potential antidote in vivo and also allowing its sensitive detection in biological samples. To further analyze the mode of ligand recognition, the crystal structure of Colchicalin is now reported in its unliganded form and is compared with the colchicine complex. A superposition of the protein structures revealed major rearrangements in the four structurally variable loops of the engineered lipocalin. Notably, the binding pocket in the unbound protein is largely occupied by the inward-bent loop #3, in particular Ile97, as well as by the phenylalanine side chain at position 71 in loop #2. Upon binding of colchicine, a dramatic shift of loop #3 by up to 11.1 Å occurs, in combination with a side-chain flip of Phe71, thus liberating the necessary space within the ligand pocket. Interestingly, the proline residue at the neighboring position 72, which arose during the combinatorial engineering of Colchicalin, remained in a cis configuration in both structures. These findings provide a striking example of a conformational adaptation mechanism, which is a long-known phenomenon for antibodies in immunochemistry, during the recognition of a small ligand by an engineered lipocalin, thus illustrating the general similarity between the mode of antigen/ligand binding by immunoglobulins and lipocalins.

Development of immunoassay based on rational hapten design for sensitive detection of pendimethalin in environment

Pendimethalin (PND) is one of the most widely used selective herbicides, but it is considered a potential human carcinogen and persistent bioaccumulative toxic chemical. Herein, five haptens with carboxylic groups were synthesized based on rational design and used to immunize mice, respectively. Then the antibodies obtained were evaluated systematically, and an indirect competitive ELISA (ic-ELISA) was developed based on an anti-PND monoclonal antibody. The 50% inhibition concentration and limit of detection of ic-ELISA were 0.53 ng/mL and 0.07 ng/mL, respectively. The cross-reactivities of ic-ELISA for the analogs of PND were ≤ 1.1%. The average recoveries of PND ranged from 79.5% to 107.4% in spiked samples. A good correlation was achieved between the ic-ELISA results and UPLC-MS/MS results in the analysis of blind samples. Thus, this assay provides a rapid and accurate tool for the determination of PND in the agro-products and agricultural producing environment.

Highly efficient and precise two-step cell selection method for tetramethylenedisulfotetramine-specific monoclonal antibody production

Monoclonal antibodies (mAbs) are useful biological tools for research, diagnostics, and pharmaceuticals. Here, we proposed a new mAb discovery platform named the two-step cell selection method (TCSM) for mAbs production of some small molecule haptens as antibiotic, toxins, and pesticides. The first step was performed by a fluorescence-activated cell sorter to enrich the hapten-specific B cells, the second step was an image-based precise pick of single hapten-specific hybridoma cells by confocal laser scanning microscopy. In this study, we used tetramethylenedisulfotetramine (TETS) as a model analyte, which is a highly lethal neurotoxic rodenticide. The TETS-specific hybridoma cells selection was completed within 10 days by the TCSM, compared with at least 40 days in the traditional hybridoma method (THM). The half maximal inhibitory concentration (IC₅₀) of the best mAb 1G6 for TETS in the TCSM was 1.98 ng mL^-1, and that of mAb 2B6 in the THM was 11.49 ng mL^-1. Antibody-TETS recognition also showed more interactions in mAb 1G6 than in mAb 2B6. Then, the mAb 1G6 was then successfully applied to develop an icELISA for TETS in biological samples with satisfactory sensitivity, accuracy and precision. The results demonstrated that the TCSM was a feasible and efficient method for mAb discovering of poisonous hapten molecules.