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Recently, phage display technology has been announced as the recipient of Nobel Prize in Chemistry 2018. Phage display technique allows high affinity target-binding peptides to be selected from a complex mixture pool of billions of displayed peptides on phage in a combinatorial library and could be further enriched through the biopanning process; proving to be a powerful technique in the screening of peptide with high affinity and selectivity. In this review, we will first discuss the modifications in phage display techniques used to isolate various cancer-specific ligands by in situ, in vitro, in vivo, and ex vivo screening methods. We will then discuss prominent examples of solid tumor targeting-peptides; namely peptide targeting tumor vasculature, tumor microenvironment (TME) and overexpressed receptors on cancer cells identified through phage display screening. We will also discuss the current challenges and future outlook for targeting peptidebased therapeutics in the clinics.

Bacterial surface (S) layers are the outermost proteinaceous cell envelope structures found on members of nearly all taxonomic groups of bacteria and Archaea . They are composed of numerous identical subunits forming a symmetric, porous, lattice-like layer that completely covers the cell surface. The subunits are held together and attached to cell wall carbohydrates by non-covalent interactions, and they spontaneously reassemble in vitro by an entropy-driven process. Due to the low amino acid sequence similarity among S-layer proteins in general, verification of the presence of an S-layer on the bacterial cell surface usually requires electron microscopy. In lactobacilli, S-layer proteins have been detected on many but not all species. Lactobacillus S-layer proteins differ from those of other bacteria in their smaller size and high predicted p I . The positive charge in Lactobacillus S-layer proteins is concentrated in the more conserved cell wall binding domain, which can be either N- or C-terminal depending on the species. The more variable domain is responsible for the self-assembly of the monomers to a periodic structure. The biological functions of Lactobacillus S-layer proteins are poorly understood, but in some species S-layer proteins mediate bacterial adherence to host cells or extracellular matrix proteins or have protective or enzymatic functions. Lactobacillus S-layer proteins show potential for use as antigen carriers in live oral vaccine design because of their adhesive and immunomodulatory properties and the general non-pathogenicity of the species.

Molecules that covalently bind macromolecular targets have found widespread applications as activity-based probes and as irreversibly binding drugs. However, the general reactivity of the electrophiles needed for covalent bond formation makes control of selectivity difficult. There is currently no rapid, unbiased screening method to identify new classes of covalent inhibitors from highly diverse pools of candidate molecules. Here we describe a phage display method to directly screen for ligands that bind to protein targets through covalent bond formation. This approach makes use of a reactive linker to form cyclic peptides on the phage surface while simultaneously introducing an electrophilic ‘warhead’ to covalently react with a nucleophile on the target. Using this approach, we identified cyclic peptides that irreversibly inhibited a cysteine protease and a serine hydrolase with nanomolar potency and exceptional specificity. This approach should enable rapid, unbiased screening to identify new classes of highly selective covalent inhibitors for diverse molecular targets. Covalent inhibitors with high selectivity are rapidly identified by phage display.

Recent progress in gene transfer technology enables the delivery of genes precisely to the application-relevant cell type ex vivo on cultivated primary cells or in vivo on local or systemic administration. Gene vectors based on lentiviruses or adeno-associated viruses can be engineered such that they use a cell surface marker of choice for cell entry instead of their natural receptors. Binding to the surface marker is mediated by a targeting ligand displayed on the vector particle surface, which can be a peptide, single-chain antibody, or designed ankyrin repeat protein. Examples include vectors that deliver genes to specialized endothelial cells or lymphocytes, tumor cells, or particular cells of the nervous system with potential applications in gene function studies and molecular medicine. Numerous receptor-targeted viral gene vectors have been described during the past years using distinct cell surface proteins for cell entry that are selectively expressed on defined cell types instead of their natural broadly expressed receptors. Receptor-targeting strategies based on directed evolution or rational engineering have been established. The latter is equally applicable to non-enveloped and enveloped vectors involving the destruction of natural receptor usage followed by the addition of a high-affinity ligand mediating attachment to the desired surface protein. Receptor-targeted vector particles can be as selective for their targeted cell type as antibodies for their antigen when applied systemically or locally in preclinical studies. Receptor targeting opens up novel concepts in gene therapy and the cell type-specific delivery of genetic material in life sciences.

One-half of the 2018 Nobel Prize in Chemistry was awarded jointly to George P. Smith and Sir Gregory P. Winter “for the phage display of peptides and antibodies”. This feature article summarizes significant achievements leading to the development of phage display of peptides and antibodies, where a bacteriophage is genetically modified to display peptides and proteins, with the primary aim of producing new biopharmaceuticals. These significant achievements are proven to be useful for the development of phage-based bioassays and biosensors.

The remarkable capacity of bacteria to adapt in response to selective pressures drives antimicrobial resistance. Pseudomonas aeruginosa illustrates this point, establishing chronic infections during which it evolves to survive antimicrobials and evade host defenses. Many adaptive changes occur on the P. aeruginosa cell surface but methods to identify these are limited. Here we combine phage display with high-throughput DNA sequencing to create a high throughput, multiplexed technology for surveying bacterial cell surfaces, Phage-seq. By applying phage display panning to hundreds of bacterial genotypes and analyzing the dynamics of the phage display selection process, we capture important biological information about cell surfaces. This approach also yields camelid single-domain antibodies that recognize key P. aeruginosa virulence factors on live cells. These antibodies have numerous potential applications in diagnostics and therapeutics. We propose that Phage-seq establishes a powerful paradigm for studying the bacterial cell surface by identifying and profiling many surface features in parallel. Methods to identify bacterial cell surface adaptations are limited. The authors combine phage display with high-throughput DNA sequencing to create a highly-multiplexed technology for surveying bacterial cell surfaces.

Phage display is one of the important and effective molecular biology techniques and has remained indispensable for research community since its discovery in the year 1985. As a large number of nucleotide fragments may be cloned into the phage genome, a phage library may harbour millions or sometimes billions of unique and distinctive displayed peptide ligands. The ligand–receptor interactions forming the basis of phage display have been well utilized in epitope mapping and antigen presentation on the surface of bacteriophages for screening novel vaccine candidates by using affinity selection-based strategy called biopanning. This versatile technique has been modified tremendously over last three decades, leading to generation of different platforms for combinatorial peptide display. The translation of new diagnostic tools thus developed has been used in situations arising due to pathogenic microbes, including bacteria and deadly viruses, such as Zika, Ebola, Hendra, Nipah, Hanta, MERS and SARS. In the current situation of pandemic of Coronavirus disease (COVID-19), a search for neutralizing antibodies is motivating the researchers to find therapeutic candidates against novel SARS-CoV-2. As phage display is an important technique for antibody selection, this review presents a concise summary of the very recent applications of phage display technique with a special reference to progress in diagnostics and therapeutics for coronavirus diseases. Hopefully, this technique can complement studies on host–pathogen interactions and assist novel strategies of drug discovery for coronaviruses.

Traditional lectins exhibit broad binding specificity for cell-surface carbohydrates, and generating anti-glycan antibodies is challenging due to low immunogenicity. Nevertheless, it is necessary to develop glycan binding proteins for single-cell glycosylation pathway analysis. Here, we test the hypothesis that protein engineering of mammalian glycosyltransferases can yield glycan-binding proteins with defined specificity. Introducing an H302A mutation, based on rational design, into porcine ST3Gal1 abolishes its enzymatic activity, but results in a lectin that specifically binds sialylated core-2 O-linked glycans (Neu5Acα2-3Galβ1-3[GlcNAc(β1-6)]GalNAcα). To improve binding, we develop a mammalian cell-surface display platform to screen variants. One ST3Gal1 mutant (sCore2) with three mutations, H302A/A312I/F313S exhibits enhanced binding specificity. Spectral flow cytometry and tissue microarray analysis using sCore2 reveal distinct cell- and tissue-specific sialyl core-2 staining patterns in human blood cells and paraffin-embedded tissue sections. Overall, glycosyltransferases can be engineered to generate specific glycan binding proteins, suggesting that a similar approach may be extended to other glycoenzymes. Cell surface glycans evolve during development & disease. New tools are needed to detect them. The authors show that engineering glycosyltransferases can yield new glycan binding proteins, enabling profiling of sugars on blood cells and human tissue.

Enhancing the secretion of recombinant proteins, particularly non-enzymatic proteins that predominate in food and pharmaceutic protein products, remains a significant challenge due to limitations in high-throughput screening methods. This study addresses this bottleneck by establishing a yeast surface display system in the food-grade microorganism Kluyveromyces lactis , enabling efficient display of model target proteins on the yeast cell surface. To assess its potential as a universal high-throughput screening tool for enhanced non-enzymatic protein secretion, we evaluated the consistency between protein display levels and secretion efficiency under the influence of various genetic factors. Our results revealed a strong correlation between these two properties. Furthermore, screening in a random mutagenesis library successfully identified a mutant with improved secretion. These findings demonstrate the potential of the K. lactis surface display system as a powerful and universal tool for high-throughput screening of strains with superior non-enzymatic protein secretion capacity. We believe this study could pave the way for efficient large-scale production of heterologous food and therapeutic proteins in industries. Key points • A YSD (yeast surface display) system was established in Kluyveromyces lactis • This system enables high-throughput screening of non-enzymatic protein secretion • This technology assists industrial production of food and therapeutic proteins Graphical Abstract