An antigen display system of GEM nanoparticles based on affinity peptide ligands.

Gram-positive enhancer matrix (GEM) nanoparticles are often used in mucosal immunity, preparation of subunit vaccines or as an immune adjuvant due to its good immunological activities in recent years. Here, we designed and screened out a high affinity peptide ligand PL23, which could specifically target the non-epitope region of Classic Swine Fever Virus (CSFV) E2 protein, by virtual screening technology, enzyme linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) test. The OD value of PL23 at 450 nm was reached 1.982, and the KD value of it was 90.12 nM. Its binding capacity to protein was verified by SDS-PAGE as well. PL23 was subsequently conjugated to GEM nanoparticles by dehydration synthesis generating GEM-PL23 particles, and the GEM-PL-E2 particles were assembled after incubated with CSFV E2 protein. The cytotoxic test indicated that PL23, CSFV E2 protein, GEM nanoparticles, GEM-PL23 particles and GEM-PL-E2 particles were not toxic to cells and GEM nanoparticles could significantly promote the growth of APCs at high concentration for 1 h, p<0.001. In addition, GEM nanoparticles could promote the uptake of antigen by APCs. The cytokines tests suggested that GEM-PL-E2 particles could promote innate immune responses, regulate adaptive immune responses generated by T cells and APCs, and promote the differentiation and maturation of dendritic cells without producing inflammasomes. The results of immunological activity identification showed GEM-PL-E2 particles induced higher levels of both neutralizing antibodies and anti-CSFV antibodies than CSFV E2 protein in mice. This strategy provided a new, simpler, faster and cheaper method for assembling GEM nanoparticles, using an affinity peptide ligand replaced the protein anchor (PA), and provided a better application prospect for the application of GEM particles.

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.

Structure Sensitivity of Au-TiO2 Strong Metal-Support Interactions.

Strong metal-support interactions (SMSI) is an important concept in heterogeneous catalysis. Herein, we demonstrate that the Au-TiO2 SMSI of Au/TiO2 catalysts sensitively depends on both Au nanoparticle (NP) sizes and TiO2 facets. Au NPs of ca. 5 nm are more facile undergo Au-TiO2 SMSI than those of ca. 2 nm, while TiO2 {001} and {100} facets are more facile than TiO2 {101} facets. The resulting capsulating TiO2-x overlayers on Au NPs exhibit an average oxidation state between +3 and +4 and a Au-to-TiO2-x charge transfer, which, combined with calculations, determines the Ti:O ratio as ca. 6:11. Both TiO2-x overlayers and TiO2-x -Au interface exhibit easier lattice oxygen activation and higher intrinsic activity in catalyzing low-temperature CO oxidation than the starting Au-TiO2 interface. These results advance fundamental understanding of SMSI and demonstrate engineering of metal NP size and oxide facet as an effective strategy to tune the SMSI for efficient catalysis.

DPL: a comprehensive database on sequences, structures, sources and functions of peptide ligands.

DPL (http://www.peptide-ligand.cn/) is a comprehensive database of peptide ligand (DPL). DPL1.0 holds 1044 peptide ligand entries and provides references for the study of the polypeptide platform. The data were collected from PubMed-NCBI, PDB, APD3, CAMPR3, etc. The lengths of the base sequences are varied from 3 to78. DPL database has 923 linear peptides and 88 cyclic peptides. The functions of peptides collected by DPL are very wide. It includes 540 entries of antiviral peptides (including SARS-CoV-2), 55 entries of signal peptides, 48 entries of protease inhibitors, 45 entries of anti-hypertension, 37 entries of anticancer peptides, etc. There are 270 different kinds of peptide targets. All peptides in DPL have clear binding targets. Most of the peptides and receptors have 3D structures experimentally verified or predicted by CYCLOPS, I-TASSER and SWISS-MODEL. With the rapid development of the COVID-2019 epidemic, this database also collects the research progress of peptides against coronavirus. In conclusion, DPL is a unique resource, which allows users easily to explore the targets, different structures as well as properties of peptides.

Tuning the size of photo-deposited metal nanoparticles via manipulating surface defect structures of TiO2 nanocrystals.

Here we report a new method for controlling photo-deposited metal nanoparticle size by manipulating surface defect structures of TiO2 nanocrystals. Our results demonstrate that the isolated oxygen vacancy could serve as an electron trapper while the oxygen vacancy cluster could act as an electron-hole recombination site in the photo-deposition process.