Suppose you need a peptide that binds a particular protein. A 10-residue peptide built from 20 amino acids has 20¹⁰, about 10 trillion, possible sequences. You can't make them one by one. Display technologies solve this by linking each peptide to the genetic code that makes it, so the best binders can be selected and then identified by sequencing.
The core idea: link genotype to phenotype
Every display method has the same three ingredients:
- A library of DNA encoding a huge variety of peptide sequences.
- A way to keep each peptide physically attached to the DNA or RNA that encodes it.
- A selection step: binders are captured on the target, non-binders are washed away, and the survivors are amplified and selected again.
After several rounds the pool becomes enriched for strong binders, and sequencing shows which peptides they are.
Phage display
George Smith first described phage display in 1985. Peptides are displayed on the surface of a bacteriophage, a virus that infects bacteria, by fusing their DNA to a gene for a coat protein. Each phage particle carries one peptide on its surface and the DNA for it inside. Sir Gregory Winter later adapted the method to evolve human antibodies, and the two shared the 2018 Nobel Prize in Chemistry. Phage libraries typically contain around 10⁹–10¹¹ different members.
mRNA display
Developed in 1997 by Richard Roberts and Jack Szostak, mRNA display works entirely in a test tube. A puromycin linker joins each peptide covalently to its own mRNA as it's made. Because there are no cells involved, libraries can reach 10¹²–10¹³ members, and unnatural amino acids can be built in.
Cyclic peptide display
Methods such as the RaPID system, developed in Hiroaki Suga's lab, combine mRNA display with reprogrammed genetic codes to build huge libraries of macrocyclic peptides containing non-standard building blocks. These approaches have produced binders to targets once considered "undruggable".
Other platforms
| Method | Display host | Strength |
|---|---|---|
| Phage display | Bacteriophage | Robust, cheap and widely used |
| Yeast display | Yeast cells | Can be sorted by flow cytometry for fine control |
| Ribosome display | Cell-free | Very large libraries |
| mRNA display | Cell-free | Largest libraries and unnatural amino acids |
From hit to lead
A display "hit" is only a starting point. Hits are synthesised chemically, their binding is confirmed with methods such as surface plasmon resonance, and then they're optimised for stability and selectivity. Increasingly, machine-learning models trained on sequencing data from display experiments help predict improved variants.
Related articles
- Antimicrobial peptides: an ancient defence against modern superbugs
- Cyclic peptides in nature
- From lab to licence: how peptide medicines are developed
Sources and further reading
- Smith GP. Filamentous fusion phage: novel expression vectors that display cloned antigens on the virion surface. Science 1985;228:1315–1317. doi:10.1126/science.4001944 · PMID: 4001944
- Roberts RW, Szostak JW. RNA-peptide fusions for the in vitro selection of peptides and proteins. PNAS 1997;94:12297–12302. doi:10.1073/pnas.94.23.12297 · PMID: 9356443
- Yamagishi Y et al. Natural product-like macrocyclic N-methyl-peptide inhibitors against a ubiquitin ligase uncovered from a ribosome-expressed de novo library. Chem Biol 2011;18:1562–1570. doi:10.1016/j.chembiol.2011.09.013 · PMID: 22195558
- Schumacher TNM et al. Identification of D-peptide ligands through mirror-image phage display. Science 1996;271:1854–1857. doi:10.1126/science.271.5257.1854 · PMID: 8596952
- The Nobel Prize in Chemistry 2018 (Arnold, Smith, Winter). www.nobelprize.org/prizes/chemistry/2018/summary