Identification of COVID-19 B-cell epitopes with phage-displayed peptide library

Background Coronavirus disease 19 (COVID-19) first appeared in the city of Wuhan, in the Hubei province of China. Since its emergence, the COVID-19-causing virus, SARS-CoV-2, has been rapidly transmitted around the globe, overwhelming the medical care systems in many countries and leading to more than 3.3 million deaths. Identification of immunological epitopes on the virus would be highly useful for the development of diagnostic tools and vaccines that will be critical to limiting further spread of COVID-19. Methods To find disease-specific B-cell epitopes that correspond to or mimic natural epitopes, we used phage display technology to determine the targets of specific antibodies present in the sera of immune-responsive COVID-19 patients. Enzyme-linked immunosorbent assays were further applied to assess competitive antibody binding and serological detection. VaxiJen, BepiPred-2.0 and DiscoTope 2.0 were utilized for B-cell epitope prediction. PyMOL was used for protein structural analysis. Results 36 enriched peptides were identified by biopanning with antibodies from two COVID-19 patients; the peptides 4 motifs with consensus residues corresponding to two potential B-cell epitopes on SARS-CoV-2 viral proteins. The putative epitopes and hit peptides were then synthesized for validation by competitive antibody binding and serological detection. Conclusions The identified B-cell epitopes on SARS-CoV-2 may aid investigations into COVID-19 pathogenesis and facilitate the development of epitope-based serological diagnostics and vaccines.

Generation of a novel affibody molecule targeting Chlamydia trachomatis MOMP

Chlamydia trachomatis (C. trachomatis) is the leading cause of preventable blindness worldwide and the most prevalent cause of bacterial sexually transmitted diseases. At present, there is no available vaccine, and recurrences after antibiotics treatment are substantial problems. Major outer membrane protein (MOMP) accounts for 60% of the outer mass of C. trachomatis, functioning as trimeric porin, and it is highly antigenic. Therefore, MOMP is the most promising candidate for vaccine developing and target therapy of Chlamydia. Affibody, a new class of affinity ligands derived from the Z-domain in the binding region of Staphylococcus aureus protein A, has been the focus of researchers as a viable alternative to antibodies. In this study, the MOMP-targeted affibody molecule (ZMOMP:461) was screened by phage-displayed peptide library. Further, the affinity and specificity were characterized by surface plasmon resonance (SPR) and Western blot. Immunofluorescence assay (IFA) indicated that the MOMP-binding affibody could recognize native MOMP in HeLa229 cells infected C. trachomatis. Immunoprecipitation assay confirmed further that ZMOMP:461 molecule specifically recognizes the epitope on relaxed trimer MOMP. Our findings provide strong evidence that affibody molecule (ZMOMP:461) serves as substitute for MOMP antibody for biological applications and has a great potential for delivering drugs for target therapy. Key points • We screened a novel affibody molecule ZMOMP:461 targeting Chlamydia trachomatis MOMP. • ZMOMP:461 recognizes the recombinant and native MOMP with high affinity and specificity. • ZMOMP:461 could be internalized into live target cells.

Discovery of Surfactant-Like Peptides from a Phage-Displayed Peptide Library

Peptides with specific affinities for various materials have been identified in the past three decades and utilized in materials science and engineering. A peptide’s capability to specifically interact with materials is not naturally derived but screened from a biologically constructed peptide library displayed on phages or cells. To date, due to limitations in the screening procedure, the function of screened peptides has been primarily limited to the affinity for target materials. Herein, we demonstrated the screening of surfactant-like peptides from a phage-displayed peptide library. A screened phage clone displaying a peptide showed high activity for accumulating at emulsion surfaces with certain assembled structures, resulting in stable emulsions. The surface tension for the solution of the chemically synthesized peptide decreased with increasing peptide concentration, demonstrating certain surface activity, which corresponded to the ability to decrease the surface tension of liquids (e.g., water), owing to the accumulation of molecules at the air–liquid or liquid–liquid interface. Peptides with a randomized sequence did not lower the surface tension, indicating the essential role of amino acid sequences in surface activity. Our strategy for identifying novel functional peptides from a phage-displayed peptide library can be used to expand the applicability of peptidyl materials and biosurfactants.

Antibody binding epitope Mapping (AbMap) of hundred antibodies in a single run

Antibodies play essential roles in both diagnostics and therapeutics. Epitope mapping is essential to understand how an antibody works and to protect intellectual property. Given the millions of antibodies for which epitope information is lacking, there is a need for high-throughput epitope mapping. To address this, we developed a strategy, Antibody binding epitope Mapping (AbMap), by combining a phage displayed peptide library with next generation sequencing. Using AbMap, profiles of the peptides bound by 202 antibodies were determined in a single test, and linear epitopes were identified for >50% of the antibodies. Using spike protein (S1 and S2)-enriched antibodies from the convalescent serum of one COVID-19 patient as the input, both linear and conformational epitopes of spike protein specific antibodies were identified. We defined peptide-binding profile of an antibody as the Binding Capacity (BiC). Conceptually, the BiC could serve as a systematic and functional descriptor of any antibody. Requiring at least one order of magnitude less time and money to map linear epitopes than traditional technologies, AbMap allows for high-throughput epitope mapping and creates many possibilities.