Isolation of isoform-specific binding proteins (Affimers) by phage display using negative selection.

Some 30 years after its discovery, phage display remains one of the most widely used methods of in vitro selection. Initially developed to revolutionize the generation of therapeutic antibodies, phage display is now the first choice for screening artificial binding proteins. Artificial binding proteins can be used as reagents to study protein-protein interactions, target posttranslational modifications, and distinguish between homologous proteins. They can also be used as research and affinity reagents, for diagnostic purposes, and as therapeutics. However, the ability to identify isoform-specific reagents remains highly challenging. We describe an adapted phage display protocol using an artificial binding protein (Affimer) for the selection of isoform-selective binding proteins.

Generation of specific inhibitors of SUMO-1- and SUMO-2/3-mediated protein-protein interactions using Affimer (Adhiron) technology.

Because protein-protein interactions underpin most biological processes, developing tools that target them to understand their function or to inform the development of therapeutics is an important task. SUMOylation is the posttranslational covalent attachment of proteins in the SUMO family (SUMO-1, SUMO-2, or SUMO-3), and it regulates numerous cellular pathways. SUMOylated proteins are recognized by proteins with SUMO-interaction motifs (SIMs) that facilitate noncovalent interactions with SUMO. We describe the use of the Affimer system of peptide display for the rapid isolation of synthetic binding proteins that inhibit SUMO-dependent protein-protein interactions mediated by SIMs both in vitro and in cells. Crucially, these synthetic proteins did not prevent SUMO conjugation either in vitro or in cell-based systems, enabling the specific analysis of SUMO-mediated protein-protein interactions. Furthermore, through structural analysis and molecular modeling, we explored the molecular mechanisms that may underlie their specificity in interfering with either SUMO-1-mediated interactions or interactions mediated by either SUMO-2 or SUMO-3. Not only will these reagents enable investigation of the biological roles of SUMOylation, but the Affimer technology used to generate these synthetic binding proteins could also be exploited to design or validate reagents or therapeutics that target other protein-protein interactions.