DARPins (an acronym for designed ankyrin repeat proteins) are genetically engineered antibody mimetic proteins typically exhibiting highly specific and high-affinity target protein binding. They are derived from natural ankyrin proteins, one of the most common classes of binding proteins in nature, which are responsible for diverse functions such as cell signaling, regulation and structural integrity of the cell. DARPins consist of at least three, repeat motifs proteins, and usually consist of four or five. Their molecular mass is about 14 or 18 kDa (kilodaltons) for four- or five-repeat DARPins, respectively.
DARPins constitute a new class of potent, specific and versatile small-protein therapies, and are used as investigational tools in various research, diagnostic and therapeutic applications. Molecular Partners AG, a clinical-stage biopharmaceutical company that is investigating these molecules, has several DARPin molecules in clinical and preclinical development.
1 Origin, structure and generation
2 Properties and potential benefits of DARPins
3 Clinical development and applications
Origin, structure and generation
A DARPin with five ankyrin repeat motifs (PDB: 2QYJ)
The DARPin platform was discovered and developed in the laboratory of Andreas Plückthun at the University of Zurich, Switzerland while studying engineering and libraries of recombinant antibodies. DARPins are derived from naturally occurring ankyrin proteins, a protein class that mediates high-affinity protein-protein interactions in nature.
DARPin libraries were designed via sequence alignments of several thousand natural ankyrin repeat motifs (of about 33 amino acids each) combined with structure-based design and recombinant DNA methods. These proteins consist of repetitive structural units that form a stable protein domain with a large potential target interaction surface. Typically, DARPins comprise four or five repeats, of which the first (N-capping repeat) and last (C-capping repeat) serve to provide a hydrophilic surface. DARPins correspond to the average size of natural ankyrin repeat protein domains. Proteins with fewer than three repeats (i.e., the capping repeats and one internal repeat) do not form a stable enough tertiary structure. The molecular mass of a DARPin depends on the total number of repeats, as shown in the following chart:
Approximate mass (kDa)