Identification of affinity-optimized peptide binders of a viral protease for chemical genetic applications.

Chemically-controlled genetic tools are useful for studying biological systems due to their ability to dose-dependently and temporally modulate intracellular function. Chemically-disrupted proximity (CDP) systems, which involve the pre-localization of two interacting protein components that can be disrupted with a small molecule, are complementary to more commonly used chemically-inducible dimerization (CID) systems. However, fewer CDP systems have been developed, and the genetically-encoded protein components have not been as optimized for intracellular applications. Here, we describe a transcriptional activation reporter assay for screening the intracellular interaction between the 21-amino acid peptide ANR and HCVp NS3a, which are the genetically-encoded components of a CDP system that utilizes clinically-approved antiviral drugs. We used this assay to screen a library of single amino acid substitution ANR variants and identified several that increase the intracellular interaction between ANR and NS3a. By combining affinity-optimized single substitutions, we achieved improved transcriptional activation and engineered an autoinhibited signaling switch with low basal activity. Together, our study describes a functional assay for screening genetically-encoded CDP components and a more optimized version of ANR for intracellular applications.