Click display: a rapid and efficient in vitro protein display method for directed evolution

We describe a novel method for in vitro protein display-click display-that does not depend on maintaining RNA integrity during biopanning and yields covalently linked protein-cDNA complexes from double-stranded input DNA within 2 h. The display is achieved in a one-pot format encompassing transcription, translation and reverse transcription reactions in series. Stable linkage between proteins and the encoding cDNA is mediated by a modified DNA linker-ML-generated via a click chemistry reaction between a puromycin-containing oligo and a cDNA synthesis primer. Biopanning of a click-displayed mock library coupled with next-generation sequencing analysis revealed >600-fold enrichment of target binders within a single round of panning. A synthetic library of Designed Ankyrin Repeat Proteins (DARPins) with & SIM;10(12) individual members was generated using click display in a 25-& mu;l reaction and six rounds of library panning against a model protein yielded a panel of nanomolar binders. This study establishes click display as a powerful tool for protein binder discovery/engineering and provides a convenient platform for in vitro biopanning selection even in RNase-rich environments such as on whole cells.

Automated summary

We describe a novel method, click display, for in vitro protein display that does not rely on RNA integrity and can produce covalently linked protein-cDNA complexes from double-stranded input DNA within 2 hours. This method combines transcription, translation, and reverse transcription reactions to achieve stable linkage between proteins and encoding cDNA using a modified DNA linker generated through click chemistry. Biopanning with a click-displayed mock library revealed significant enrichment of target binders in just one round. A synthetic library of DARPins generated using click display and subjected to six rounds of panning yielded a panel of nanomolar binders, showcasing the power and convenience of this method even in RNase-rich environments.