Engineering an autonomous VH domain to modulate intracellular pathways and to interrogate the eIF4F complex.

An attractive approach to target intracellular macromolecular interfaces and to model putative drug interactions is to design small high-affinity proteins. Variable domains of the immunoglobulin heavy chain (VH domains) are ideal miniproteins, but their development has been restricted by poor intracellular stability and expression. Here we show that an autonomous and disufhide-free VH domain is suitable for intracellular studies and use it to construct a high-diversity phage display library. Using this library and affinity maturation techniques we identify VH domains with picomolar affinity against eIF4E, a protein commonly hyper-activated in cancer. We demonstrate that these molecules interact with eIF4E at the eIF4G binding site via a distinct structural pose. Intracellular overexpression of these miniproteins reduce cellular proliferation and expression of malignancy-related proteins in cancer cell lines. The linkage of high-diversity in vitro libraries with an intracellularly expressible miniprotein scaffold will facilitate the discovery of VH domains suitable for intracellular applications.

Engineering protein thermostability using a generic activity-independent biophysical screen inside the cell.

Protein stability is often a limiting factor in the development of commercial proteins and biopharmaceuticals, as well as for biochemical and structural studies. Unfortunately, identifying stabilizing mutations is not trivial since most are neutral or deleterious. Here we describe a high-throughput colony-based stability screen, which is a direct and biophysical read-out of intrinsic protein stability in contrast to traditional indirect activity-based methods. By combining the method with a random mutagenesis procedure, we successfully identify thermostable variants from 10 diverse and challenging proteins, including several biotechnologically important proteins such as a single-chain antibody, a commercial enzyme and an FDA-approved protein drug. We also show that thermostabilization of a protein drug using our approach translates into dramatic improvements in long-term stability. As the method is generic and activity independent, it can easily be applied to a wide range of proteins.