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.

Isolation and Characterizations of A Novel Recombinant scFv Antibody Against Exotoxin-A of Pseudomonas Aeruginosa

Background: Pseudomonas aeruginosa is known as the leading cause of nosocomial infections especially in people with a compromised immune system. Targeting virulence factors by neutralizing antibodies is a novel paradigm for the treatment of antibiotic-resistant pseudomonas infections.Methods: In this respect, exotoxin A is one of the most potent virulence factors in P. aeruginosa. The present study was conducted to identify a novel human scFv antibody against domain I of P. aeruginosa exotoxin A from a human scFv phage library. For this, the recombinant domain I of exotoxin A was expressed in E. coli and purified by Ni-NTA column. A novel screening procedure was conducted to prevent the elimination of rare specific clones. Based on polyclonal phage ELISA results, the fifth round of biopanning was selected to identify specific phage clones.Results: Two positive clones were found by monoclonal phage. The phage clone with high reactivity was evaluated by ELISA and western blot. The purified scFv also showed high reactivity with full length exotoxin.Conclusions: In conclusion, the purified anti-exotoxin A scFv displayed high specificity against exotoxin A. The human scFv identified can be the groundwork for development of a novel therapeutic agent for control of P. aeruginosa infections.

Camelid VHHs Fused to Human Fc Fragments Provide Long Term Protection Against Botulinum Neurotoxin A in Mice

The bacterium Clostridium botulinum is the causative agent of botulism—a severe intoxication caused by botulinum neurotoxin (BoNT) and characterized by damage to the nervous system. In an effort to develop novel C. botulinum immunotherapeutics, camelid single-domain antibodies (sdAbs, VHHs, or nanobodies) could be used due to their unique structure and characteristics. In this study, VHHs were produced using phage display technology. A total of 15 different monoclonal VHHs were selected based on their comlementarity-determining region 3 (CDR3) sequences. Different toxin lethal dose (LD50) challenges with each selected phage clone were conducted in vivo to check their neutralizing potency. We demonstrated that modification of neutralizing VHHs with a human immunoglobulin G (IgG)1 Fc (fragment crystallizable) fragment (fusionbody, VHH-Fc) significantly increased the circulation time in the blood (up to 14 days). At the same time, VHH-Fc showed the protective activity 1000 times higher than monomeric form when challenged with 5 LD50. Moreover, VHH-Fcs remained protective even 14 days after antibody administration. These results indicate that this VHH-Fc could be used as an effective long term antitoxin protection against botulinum type A.

Improved Analysis of Phage ImmunoPrecipitation Sequencing (PhIP-Seq) Data Using a Z-score Algorithm

Phage ImmunoPrecipitation Sequencing (PhIP-Seq) is a massively multiplexed, phage-display based methodology for analyzing antibody binding specificities, with several advantages over existing techniques, including the uniformity and completeness of proteomic libraries, as well as high sample throughput and low cost. Data generated by the PhIP-Seq assay are unique in many ways. The only published analytical approach for these data suffers from important limitations. Here, we propose a new statistical framework with several improvements. Using a set of replicate mock immunoprecipitations (negative controls lacking antibody input) to generate background binding distributions, we establish a statistical model to quantify antibody-dependent changes in phage clone abundance. Our approach incorporates robust regression of experimental samples against the mock IPs as a means to calculate the expected phage clone abundance, and provides a generalized model for calculating each clone’s expected abundance-associated standard deviation. In terms of bias removal and detection sensitivity, we demonstrate that this z-score algorithm outperforms the previous approach. Further, in a large cohort of autoantibody-defined Sjögren’s Syndrome (SS) patient sera, PhIP-Seq robustly identified Ro52, Ro60, and SSB/La as known autoantigens associated with SS. In an effort to identify novel SS-specific binding specificities, SS z-scores were compared with z-scores obtained by screening Ropositive sera from patients with systemic lupus erythematosus (SLE). This analysis did not yield any commonly targeted SS-specific autoantigens, suggesting that if they exist at all, their epitopes are likely to be discontinuous or post-translationally modified. In summary, we have developed an improved algorithm for PhIP-Seq data analysis, which was validated using a large set of sera with clinically characterized autoantibodies. This z-score approach will substantially improve the ability of PhIP-Seq to detect and interpret antibody binding specificities. The associated Python code is freely available for download here: https://github.com/LarmanLab/PhIP-Seq-Analyzer.

Esterase 1 is a Novel Transcriptional Repressor of Growth Hormone Receptor Gene Expression: A Unique Noncatalytic Role for a Carboxyesterase Protein

The pleiotropic actions of GH result from its engagement with the GH receptor (GHR). GHR expression is regulated by free fatty acids (FFA). A cDNA phage expression library was screened to identify a phage clone expressing esterase 1 (ES1) binding to the FFA-response element (FARE), L2-D1, in the murine GHR promoter. Ectopically expressed ES1 inhibited GHR promoter activity via effects at two FARE, L2-D1 and L2-A2. Chromatin immunoprecipitation experiments demonstrated specific association of ES1 with the FARE. Catalytically inactive ES1 retained inhibitory activity on the GHR promoter and excluded the possibility that the effect on the GHR promoter was an indirect effect secondary to ES1's actions on the intracellular metabolism of FFA. Ectopically expressed ES1 inhibited the endogenous GHR mRNA and protein expression in 3T3-F442A preadipocytes. Subcellular fractionation and confocal microscopy established that ES1 localizes both to the cytoplasm and the nucleus. Experiments demonstrated chromosome region maintenance 1-dependent nuclear export and the presence of a functional nuclear export signal in ES1. The domain of ES1 responsible for the effect on the GHR promoter was localized to the C-terminal portion of the protein. The in vivo significance of ES1's effect on GHR expression was suggested by decreased liver GHR mRNA expression in mice on a high-fat diet correlating with increased steady-state abundance of liver ES1 mRNA. Our results identify and characterize ES1 as a novel transcriptional regulator of GHR gene expression, thereby establishing a unique nonenzymatic role for a carboxyesterase and expanding the potential biological roles of this protein superfamily.

Staphylococcus Aureus Detection In Platelets Using Short Synthetic Peptides Derived From Phage-Displayed Random Peptide Libraries Coupled with Quantum-Dot Nanocrystals

Abstract 3359 Introduction: Bacterial sepsis in recipients of transfusion products due to contamination of blood components is an infrequent but serious and potentially a fatal complication. Unlike red cells, platelet concentrates (PC) are stored for up to 5 days at room temperature after collection, which is conducive for bacterial growth. In 42% of the sepsis cases following PCs, the most common bacterial contaminant is Staphylococcus spp. Timely detection of these contaminated units is a public health priority. Although a multitude of bacterial diagnostic tests are available for PCs, still there is a need for developing more sensitive, specific and rapid detection assays. The primary objective of this study is to develop a simple and highly sensitive procedure that facilitates rapid and enhanced detection of bacteria using Staphylococcus aureus as a model for PCs. Methods: A commercially available bacteriophage-displayed random 12-mer peptide library was screened against S. aureus. The screening and subsequent sequencing of the phage DNA identified a phage clone containing a coding sequence for 12-amino acid peptide that selectively binds to S. aureus. We assessed the binding specificity and detection sensitivity of the peptide to a panel of six bacteria spiked in platelets (including S. aureus) by dot blot, ELISA and fluorometry. The peptides were further labeled with streptavidin-conjugated fluorescent Nanocrystal quantum-dots (Q-dots) to enhance the sensitivity of the assay. Results: The membrane-based dot blot method revealed that the peptide binds specifically to S. aureus. ELISA and fluorometry analysis of spiked platelet samples revealed that the peptide binds to S. aureus at 103 CFU/ml concentrations. By using the peptide-Nanocrystal Q-dot combination (peptide probes), the detection sensitivity was further enhanced. The peptide binding remained relatively constant between pH 5 to 7.5. Conclusion: This model system demonstrates that peptides derived from random phage library in combination with Nanocrystal Q-dots facilitate high sensitivity detection of S. aureus. In general, this study provides a proof-of-concept that ‘peptide probes' selected against specific bacteria are useful in detecting and monitoring them in various settings relevant to blood safety and transfusion medicine. The findings and conclusions in this abstract have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy. Disclosures: No relevant conflicts of interest to declare.

The mechanism by which molecules containing the HIV gp41 core-binding motif HXXNPF inhibit HIV-1 envelope glycoprotein-mediated syncytium formation

The HIV-1 gp41 (glycoprotein 41) core plays a critical role in fusion between the viral and target cell membranes. We previously identified a gp41 core-binding motif, HXXNPF, by screening the phage display peptide libraries. In the present study, we elucidated the mechanism of action of HXXNPF motif-containing molecules of different sizes, including the phage clone L7.8 (a selected positive phage clone), L7.8-g3p* (a 10–kDa fragment of the gene 3 protein) and JCH-4 (a peptide containing 13 residues of L7.8-g3p*), regarding their respective binding abilities to the six-helix bundle and inhibition on syncytium formation at different temperatures. We found that all of the HXXNPF motif-containing molecules could bind to the gp41 core, and that their binding sites may be located in the N-helix domain. L7.8-g3p* and JCH-4 effectively inhibited HIV-1 Env (envelope glycoprotein)-mediated syncytium formation at 37 °C, while the phage clone L7.8 showed no inhibition under the same conditions. However, at suboptimal temperature (31.5 °C), all of these HXXNPF motif-containing molecules were capable of inhibiting syncytium formation. These results suggest that these HXXNPF motif-containing molecules mainly bind to the gp41 core and stop the fusion process mediated by the fusion-active core, resulting in inhibition of HIV-1 fusion and entry. The HXXNPF motif-containing molecules may be used as probes for studying the role of the HIV-1 gp41 core in the late stage of the membrane-fusion process.

Cloning, Characterization, and Expression of Bartonella henselae p26

ABSTRACT In order to identify immunoreactive Bartonella henselae proteins, B. henselae antiserum from an experimentally infected cat was used to screen a B. henselae genomic DNA expression library. One immunoreactive phage clone contained a gene (p26) with significant nucleotide identity with orthologs in brucellae, bartonellae, and several plant-associated bacteria. p26 gene sequences from four B. henselae strains, one B. koehlerae strain, and one B. clarridgeiae strain were cloned. Comparative nucleotide sequence analysis showed that p26 is a potential marker for molecular diagnosis of infection, as well as for identification to species level and genotyping of Bartonella sp. isolates. Alignment of the predicted amino acid sequences illustrated conserved putative protein features including a hydrophobic transmembrane region, a peptide cleavage site, and four dominant antigenic sites. Expression of p26 in Escherichia coli produced two proteins (26 and 27.5 kDa), both of which were reactive with feline anti-B. henselae antisera. Furthermore, murine hyperimmune serum raised against either recombinant protein reacted with both proteins. No reactivity to either recombinant protein was detected in nonimmune serum, and reactivity persisted as long as 20 weeks for one cat. The p26 protein product is an immunodominant antigen that is expressed during infection in cats as a preprotein and is subsequently cleaved to form mature P26.

Selection of peptides recognized by human antibodies against the surface ofPlasmodium falciparum-infected erythrocytes

In an attempt to identify mimotopes of the surface antigens ofP. falciparum-infected erythrocytes (iRBC), antibodies were eluted from iRBC that had been treated with a pool of sera from malaria-infected individuals (IHS), and were used to screen a phage display library (PDL). After repeated panning of the PDL on immobilized antibodies, phage that selectively bound to IHS were accumulated. Of 23 randomly chosen clones that were sequenced, 13 individual sequences were detected at varying frequencies and 3 of the 13 sequences had homology with membrane proteins known to exist on iRBC. The majority of phage clones (7 out of 8 clones) selected after the 4th panning bound selectively to IgG in IHS. Specific binding of the selected phage to IgG in IHS was also confirmed using 24 IHS and 11 sera from uninfected individuals. One phage clone was the most frequently found in the sequenced clones after the 4th panning, and the binding of this clone to IgG in all IHS was greater than in any serum from uninfected individuals. A rabbit antiserum against the peptide expressed on the clone specifically recognized the surface of iRBC and resulted in iRBC haemolysis.

Mapping of a dengue virus neutralizing epitope critical for the infectivity of all serotypes: insight into the neutralization mechanism

Dengue virus infections are a growing public health concern and strategies to control the spread of the virus are urgently needed. The murine monoclonal antibody 4E11 might be of interest, since it neutralizes dengue viruses of all serotypes by binding to the 296–400 segment of the major dengue virus envelope glycoprotein (DE). When phage-displayed peptide libraries were screened by affinity for 4E11, phage clone C1 was selected with a 50% frequency. C1 shared three of nine residues with DE306–314 and showed significant reactivity to 4E11 in ELISA. C1-induced antibodies cross-reacted with DE296–400 in mice, suggesting that it was a structural equivalent of the native epitope of 4E11 on DE. Accordingly, 4E11 bound to the DE306–314 synthetic peptide and this reaction was inhibited by DE296–400. Moreover, DE306–314 could block dengue virus infection of target cells in an in vitro assay. A three-dimensional model of DE revealed that the three amino acids shared by DE296–400 and C1 were exposed to the solvent and suggested that most of the amino acids comprising the 4E11 epitope were located in the DE306–314 region. Since 4E11 blocked the binding of DE296–400 to heparin, which is a highly sulfated heparan sulfate (HSHS) molecule, 4E11 may act by neutralizing the interaction of DE306–314 with target cell-displayed HSHS. Our data suggest that the DE306–314 segment is critical for the infectivity of all dengue virus serotypes and that molecules that block the binding of DE306–314 to HSHS may be antiviral reagents of therapeutic interest.