Abstract
<jats:p>Peptides and proteins represent a diverse and highly versatile class of biomolecules with applications spanning therapeutics, diagnostics, and biotechnology. Their structural complexity, high specificity, and broad functional potential make them attractive targets for molecular discovery. A powerful strategy for identifying novel functional peptides and proteins involves genetically encoded display technologies such as phage, mRNA, or cell surface display. These methods couple genotype to phenotype, and by this genetic encoding of the sequence information enable very high-throughput in vitro or in vivo selection from vast libraries. In this review, we cover methods by which chemical diversity can be increased in these genetically-encoded display settings. We first give an overview of approaches for genetic code reprogramming and expansion that are compatible with both cellular as well as in vitro translation. We then survey the use of chemical and enzymatic diversification reactions employed across different display systems, giving an outline of the system, its relative strengths and weaknesses, and detail reactions that have been exploited in that setting. We also indicate scope for expanding these reactions, and discuss how synergy between genetic code expansion and/or reprogramming with subsequent chemical or enzymatic modification allows access to an even broader chemical space. For each display approach, examples are given of hits found using these diversification approaches to emphasise what can be gained. With this we hope to illustrate the scope of what is possible, and especially to stimulate further uptake of such methods within biomolecule discovery campaigns.</jats:p>