A universal method for surface-based binding assays by preparing immobilized ß2-adrenergic receptor stationary phase using solid binding peptide as a fusion tag.

Protein functionalized surface has the potential to develop new assays for determining the drug-like properties of potential compounds and discovering specific partners of G protein-coupled receptors (GPCRs). However, a universal method for purifying and immobilizing functional GPCRs has remained elusive. To this end, we developed a general and rapid way to purify and immobilize ß2-adrenergic receptor (ß2AR) by silicon-specific peptide. We screened CotB1p as a tag from six silica-binding peptides (minTBP-1, CotB1p, SB7, Car9, and Si4-1) by examining their affinity to macroporous silica gel. We investigated the adsorption and desorption of CotB1p-tagged ß2-adrenoceptor (ß2AR-CotB1p) under diverse conditions to propose a protocol for receptor purification and immobilization. Under optimized conditions, ß2AR immobilization were achieved by directly immersing cell lysates harboring the receptor with silica gel, and the elution of the receptor without demonstratable contaminants was realized by including l-arginine/L-lysine in the elutes. This allows purification of the receptor from Escherichia coli (E.coli) lysates with a purity of 95 %. The immobilized receptor was utilized as a stationary phase to reveal the tag impact on ligand-binding outputs by comparing the CotB1p-strategy with a typical covalent method. The KAs of salbutamol, chlorprenaline, tulobuterol, and terbutaline on ß2AR-CotB1p column were 1.26 × 106, 6.59 × 106, 7.90 × 106, and 8.97 × 105 M-1 respectively, which were two orders of magnitude higher than those on the Halo-ß2AR column. The whole immobilization was accomplished within 30 min without the requirement of any special treatment, resulting in enhanced accuracy for determining receptor-ligand binding parameters. Taken together, CotB1p-mediated strategy is simple, rapid, and universal for purification or immobilization of unstable biomolecules like GPCRs for analytical and biological applications.

Highly efficient GPCR immobilization with enhanced fouling resistance, salt tolerance, and chromatographic performance.

The feasibility of immobilized protein-based biodetection relies critically on the activity of the immobilized proteins as well as the biocompatibility of the protein surface. Although many protein immobilization strategies have been developed with satisfied detection readout signals. Non-specific interactions caused by the protein-coating surface are still of great concern since they often interfere with or affect the reliability of detection. Herein, we developed a highly efficient G protein-coupled receptor (GPCR) immobilization method by the combination of polyethylene glycol (PEG) with a self-labeling enzyme-catalyzed reaction. The immobilization relies on the covalent interaction between the fusion tag of a target GPCR (kinase domain of epidermal growth factor receptor, EGFR) and its covalent inhibitor ibrutinib, which is modified on PEGylated silica gels. Two types of GPCRs, N-methyl-D-aspartate 2 A receptor (NMDAR2A) and endothelin A receptor (ETAR), were used as examples to realize protein immobilization. The GPCR modified gels and the affinity columns packed with them have been extensively characterized, in terms of non-specific adsorptions, retention factor (k'), half peak width (W1/2), tailing factor (Tf), theoretical plates (N), and association and dissociation constants of the ligands with the receptors. The immobilized GPCRs with reduced non-specific interactions and enhanced fouling resistance, salt tolerance, and chromatographic performance were clearly observed. We believe it is the first work to introduce PEGylation in GPCR immobilization and provide comprehensive proof-of-concept studies to illustrate the improved antifouling property, salt tolerance, and chromatographic performance. This method could be generally applicable in other immobilized protein-based technology for reliable biodetection.

Single-cell RNA sequencing reveals the dynamics and heterogeneity of lymph node immune cells during acute and chronic viral infections.

Introduction: The host immune response determines the differential outcome of acute or chronic viral infections. The comprehensive comparison of lymphoid tissue immune cells at the single-cell level between acute and chronic viral infections is largely insufficient. Methods: To explore the landscape of immune responses to acute and chronic viral infections, single-cell RNA sequencing(scRNA-seq), scTCR-seq and scBCR-seq were utilized to evaluate the longitudinal dynamics and heterogeneity of lymph node CD45+ immune cells in mouse models of acute (LCMV Armstrong) and chronic (LCMV clone 13) viral infections. Results: In contrast with acute viral infection, chronic viral infection distinctly induced more robust NK cells and plasma cells at the early stage (Day 4 post-infection) and acute stage (Day 8 post-infection), respectively. Moreover, chronic viral infection exerted decreased but aberrantly activated plasmacytoid dendritic cells (pDCs) at the acute phase. Simultaneously, there were significantly increased IgA+ plasma cells (MALT B cells) but differential usage of B-cell receptors in chronic infection. In terms of T-cell responses, Gzma-high effector-like CD8+ T cells were significantly induced at the early stage in chronic infection, which showed temporally reversed gene expression throughout viral infection and the differential usage of the most dominant TCR clonotype. Chronic infection also induced more robust CD4+ T cell responses, including follicular helper T cells (Tfh) and regulatory T cells (Treg). In addition, chronic infection compromised the TCR diversity in both CD8+ and CD4+ T cells. Discussion: In conclusion, gene expression and TCR/BCR immune repertoire profiling at the single-cell level in this study provide new insights into the dynamic and differential immune responses to acute and chronic viral infections.

3D collagen porous scaffold carrying PLGA-PTX/SDF-1α recruits and promotes neural stem cell differentiation for spinal cord injury repair.

Spinal Cord Injury (SCI), one of the major factors of disability, can cause irreversible motor and sensory impairment. There are no effective therapeutic drugs and technologies available in domestic or foreign countries currently. Neural stem cells (NSCs), with the potential for multidirectional differentiation, are a potential treatment for SCI. However, it has been demonstrated that NSCs primarily differentiated into astrocytes rather than neurons due to the inflammatory microenvironment, and the current challenge remains to direct the differentiation of NSCs into neurons in the lesion site. It was reported that the microtubule-stabilizing agent paclitaxel (PTX) was able to promote the differentiation of NSCs into neurons rather than astrocytes after SCI. SDF-1α can recruit NSCs and thus guide the migration of stem cells. In this study, we developed a functional collagen scaffold by loading SDF-1α and nanoparticle-encapsulated PLGA-PTX into a 3D collagen porous scaffold, allowing for slow release of PTX. When the functional scaffolds were implanted into the injury site, it provided a neural regeneration conduit channel for the migration of NSCs and neuronal differentiation. Neural regeneration promoted the recovery of motor function and reduced glial scar formation after SCI. In conclusion, a 3D collagen porous scaffold combined with PLGA-PTX and SDF-1α is a promising therapeutic strategy for SCI repair.

Affinity Chromatographic Method for Determining Drug-Protein Interaction with Enhanced Speed Than Typical Frontal Analysis.

Revealing drug-protein interaction is highly important to select a drug candidate with improved drug-like properties in the early stages of drug discovery. This highlights the urgent need to develop assays that enable the analysis of drug-protein interaction with high speed. Herein, this purpose was realized by the development of an affinity chromatographic method with a two-fold higher speed than typical assays like frontal analysis and zonal elution. The method involved synthesis of a stationary phase by immobilizing poly(ADP-ribose) polymerase-1 (PARP1) onto macroporous silica gel through a one-step bioorthogonal reaction, characterization of mutual displacement interaction of two canonical drugs to the immobilized PARP1, determination of the interaction between three (iniparib, rucaparib, and olaparib) drugs and the protein, and validation of these parameters by typical frontal analysis. The numbers of binding sites on the column were (2.85 ± 0.05) × 10-7, (1.89 ± 0.71) × 10-6, and (1.49 ± 0.06) × 10-7 M for iniparib, rucaparib, and olaparib, respectively. On these sites, the association constants of the three drugs to the protein were (9.85 ± 0.56) × 104, (2.85 ± 0.34) × 104, and (1.07 ± 0.35) × 105 M-1. The determined parameters presented a good agreement with the calculation by typical frontal analyses, which indicated that the current continuous competitive frontal analysis method was reliable for determining drug-protein interaction. Application of the methods was achieved by screening tubeimosides I and II as the bioactive compounds against breast cancer in Bolbostemma paniculatum. Their mechanism may be the interference of DNA repair via down-regulating PARP1 and meiotic recombination 11 expressions, thus leading to oncogene mutations and death of cancer cells. The method was high speed since it allowed simultaneous determination of binding parameters between two drugs and a protein with a smaller number of experiments to be performed. Such a feature made the method an attractive alternative for high-speed analysis of drug-protein interaction or the other bindings in a binary system.

Stepwise Frontal Analysis Coupled with Affinity Chromatography: A Fast and Reliable Method for Potential Ligand Isolation and Evaluation from Mahuang-Fuzi-Xixin Decoction.

Mahuang-Fuzi-Xixin Decoction (MFXD) is widely used in the treatment of asthma, however, the functional components in the decoction targeting beta2-adrenoceptor (ß2 -AR) remain unclear. Herein, we immobilized the haloalkane dehalogenase (Halo)-tagged ß2 -AR on the 6-chlorocaproic acid-modified microspheres. Using the affinity stationary phase, the interactions of four ligands with the receptor were analyzed by stepwise frontal analysis. The association constants were (4.75±0.28)×104  M-1 for salbutamol, (2.93±0.15)×104  M-1 for terbutaline, (1.23±0.03)×104  M-1 for methoxyphenamine, (5.67±0.38)×104  M-1 for clorprenaline at high-affinity binding site, and (2.73±0.05)×103  M-1 at low-affinity binding site. These association constants showed the same rank order as the radioligand binding assay, demonstrating that immobilized ß2 -AR had capacity to screen bioactive compounds binding to the receptor while stepwise frontal analysis could predict their binding affinities. Application of the immobilized receptor in analysis of MFXD by chromatographic method revealed that ephedrine, aconifine, karakoline, and chasmanine were the bioactive compounds targeting ß2 -AR. Among them, ephedrine and chasmanine exhibited association constants of (2.94±0.02)×104 M-1 and (4.60±0.15)×104  M-1 to the receptor by stepwise frontal analysis. Molecular docking analysis demonstrated that ephedrine, chasmanine, and the other two compounds interact with ß2 -AR through the same pocket involving the key amino acids such as Asn312, Asp113, Phe289, Trp286, Tyr316, and Val114. As such, we reasoned that the four compounds dominate the therapeutic effect of MFXD against asthma through ß2 -AR mediating pathway. This work shed light on the potential of immobilized ß2 -AR for drug discovery and provided a valuable methodology for rapid screening.

Rapid separation and binding configuration prediction of the components in Danshen decoction to endothelin A receptor using affinity chromatography and molecular dynamics simulation.

As a famous traditional Chinese formula, Danshen Decoction has the potential to relieve the pain of pulmonary arterial hypertension patients, however, the functional components remain unknown. Herein, we reported a method to screen the functional components in Danshen Decoction targeting endothelin receptor A, an accepted target for the treatment of the disease. The receptor was functionalized on the macroporous silica gel through an epidermal growth factor receptor fusion tag and its covalent inhibitor. Using the affinity gel as the stationary phase, the bioactive compound was identified as salvianolic acid B by mass spectrometry. The binding kinetic parameter (dissociation rate constants kd ) of salvianolic acid B with the receptor was determined via peak profiling. Using the specific ligands of the receptor as probes, the binding configuration prediction of salvianolic acid B with the receptor was performed by molecular dynamics simulation. Our results indicated that salvianolic acid B is a potential bioactive compound in Danshen Decoction targeting the receptor. This work showed that receptor chromatography in combination with molecular dynamics simulation is applicable to predicting the binding kinetics and configuration of a ligand to a receptor, providing crucial insight for the rational design of drugs that recognize functional proteins.

Enhancing Chromatographic Performance of Immobilized Angiotensin II Type 1 Receptor by Strain-Promoted Alkyne Azide Cycloaddition through Genetically Encoded Unnatural Amino Acid.

During integration to the solid surface, the effects of tags introduced for bioorthogonal reactions on protein activity have received far less investigation. This represents the major challenge of improving the performance of the immobilized protein-based assays. Herein, the relationship between the fusion tags and their reaction efficiency in mediating the assay performance was realized by determining the chromatographic performance using genetically encoded azide-alkyne cycloaddition, and Halo- and SNAP-tagged bioorthogonal reactions for synthesizing immobilized angiotensin II type 1 receptor (AT1R). We demonstrated that immobilization with the incorporation of unnatural amino acid in the receptor minimizes the peak tailings and broadenings of irbesartan, fimasartan, losartan, and tasosartan, while attachment via large tags (SNAP and Halo) leads to serious asymmetry peaks. Upon the first immobilization, the association constants of the four drugs to AT1R appeared to be 1 order of magnitude greater than the other two attachments. Such enhancement is likely reasoned by the improved association rate constants and the relatively identical dissociation rates due to the small tag. While demonstrating improved chromatographic performance, the immobilized AT1R prepared by the genetically encoded azide-alkyne reaction was applied in analyzing Uncaria Schreber nom. cons. extract, which identified hynchophylline as a specific ligand binding to the receptor. As immobilized proteins move toward diverse assays, our findings provide an unprecedented insight into the relation between fusion tags and their reaction efficiency in mediating the assay performance, which is thus dedicated to the creation of a protein-functionalized surface for precisely determining the drug-protein interaction and discovering the specific partner of the protein.

Mathematical and experimental validation of an approach for simultaneously determining the binding parameters of two drugs to a receptor.

Quantifying drug-protein interactions has a pivotal role in both early phase drug development and clinical processes. Diverse affinity chromatographic methods like nonlinear chromatography can realize such quantification, however, their throughputs are challenged due to the loading of a single ligand during each run. This work derivatized a new equation for simultaneously determining the bindings of two ligands to a protein relying on assumption that the retention factors of the ligands are dependent on their injection amounts. Experimental validation of the derivatization was performed on an immobilized endothelin A receptor (ETAR) column taking ambrisentan, bosentan, and macitentan as injecting solutes. All three ligands presented a decrease in retention times along with increasing moles of injection when they were singly injected into the column. Likewise, negative relationships between the retentions and the injection amounts were observed when co-injection of ambrisentan/bosentan or bosentan/macitentan was performed, thus confirming the assumption of the derivatization. The association constants of ambrisentan, bosentan, and macitentan binding to ETAR were (1.42 ± 0.78)×104, (1.81 ± 0.22)×104, and (1.71 ± 0.41)×104 L/mol when each of them was singly loaded on the column. Such data displayed insignificant changes in four weeks thereby providing a proof of good stability of the column during the period. Co-injections of the two ligand pairs resulted in the association constants of (2.97 ± 0.13)×104 for ambrisentan, (2.51 ± 0.87)×104 for bosentan, and (2.88 ± 0.34)×104 L/mol for macitentan. These results were in good agreement with the calculation when each of the ligands was injected alone into the column and demonstrated little differences from the data by nonlinear chromatography. Owning to the simultaneous analysis of two ligands, the throughput of the proposed method was twofold higher than the typical assays including frontal analysis, zonal elution, and nonlinear chromatography. It is possible to become an alternative for rapid analysis of drug-protein interaction.