Engineering High Affinity Protein-Protein Interactions Using a High-Throughput Microcapillary Array Platform

Affinity maturation of protein protein interactions requires iterative rounds of protein library generation and high-throughput screening to identify variants that bind with increased affinity to a target of interest. We recently developed a multipurpose protein engineering platform, termed mu SCALE (Microcapillary Single Cell Analysis and Laser Extraction). This technology enables high-throughput screening of libraries of millions of cell-expressing protein variants based on their binding properties or functional activity. Here, we demonstrate the first use of the mu SCALE platform for affinity maturation of a protein protein binding, interaction. In this proof-of-concept study, we engineered an extracellular domain of the Axl receptor tyrosine kinase to bind tighter to its ligand Gas6. Within 2 weeks, two iterative rounds of library generation and screening resulted in engineered Axl variants with a 50-fold decrease in kinetic dissociation rate, highlighting the use of mu SCALE as a new tool for directed evolution.