Wikipedia
Monobodies are synthetic binding proteins that are constructed using a fibronectin type III domain (FN3) as a molecular scaffold. Monobodies are simple and robust alternative to antibodies for creating target-binding proteins. The term "monobody" was coined in 1998 by the Koide group who published the first paper demonstrating the monobody concept using the tenth FN3 domain of human fibronectin.
Monobodies are generated from combinatorial libraries in which portions of the FN3 scaffold are diversified using molecular display and directed evolution technologies such as phage display, mRNA display and yeast surface display. A large number of monobodies that have high affinity and high specificity to their respective targets have been reported.
Monobodies belong to the class of molecules collectively called antibody mimics (or Antibody mimetics) and alternative scaffolds that aim to overcome shortcomings of natural antibody molecules. A major advantage of monobodies over conventional antibodies is that monobodies can readily be used as genetically encoded intracellular inhibitors, that is you can express a monobody inhibitor in a cell of choice by simply transfecting the cell with a monobody expression vector. This is because of unique characteristics of the underlying FN3 scaffold: small (~90 residues), stable, easy to produce, and its lack of disulfide bonds that makes it possible to produce functional monobodies regardless of the redox potential of the cellular environment, including the reducing environment of the cytoplasm and nucleus. In contrast, most antibodies and antibody fragments dependend on disulfide bonds formation and they must be produced under an oxidizing environment.
The monobody technology has been adopted in the biotechnology industry, most notably by Adnexus, a biotechnology company which has been part of Bristol-Myers Squibb since 2007 under the name of Adnectins (originally as Trinectins by its predecessor, Phylos). An example is pegdinetanib (Angiocept), an antagonist of vascular endothelial growth factor receptor 2 (VEGFR-2), which has entered Phase II clinical trials investigating the treatment of glioblastoma in October 2007.