Over the last 20 years, we have developed Designed Ankyrin Repeat Proteins (DARPins) as a platform for specific binding proteins. This has meanwhile become a mature technology, which is now also used to develop therapeutics for a variety of diseases. By using consensus design, different synthetic libraries of ankyrin repeat proteins had been created. From these, the desired binders are selected by display technologies such as ribosome display.
Why are DARPins so useful? They are very stable and do not have disulfide bonds and therefore, unlike most antibodies, also work inside the cytosol. They can be prepared in very large amounts from E. coli, are very specific, and often show affinities in the picomolar range. They are obtained from synthetic libraries we have created, using technologies such as ribosome display (in a high-throughput facility), but also using phage display or yeast display.
What can you do with them? They have been used academically in a very wide spectrum of applications, ranging from crystallization chaperones, including for membrane proteins, scaffolds for electron microscopy, as intracellular inhibitors, extracellular receptor ligands, sensors, virus-retargeting adapters, or affinity ligands. Many fusion protein designs would have been difficult to achieve with recombinant antibodies, as DARPins are very resistant to aggregation and misfolding. They have also been used to study fundamental questions of protein folding and design.