Evolution of proteins with genetically encoded "chemical warheads".

We recently developed a phage-based system for the evolution of proteins in bacteria with expanded amino acid genetic codes. Here we demonstrate that the unnatural amino acid p-boronophenylalanine (BF) confers a selective advantage in the evolution of glycan-binding proteins. We show that an unbiased library of naive antibodies with NNK-randomized V(H) CDR3 loops converges upon mutants containing BF when placed under selection for binding to a model acyclic amino sugar. This work represents a first step in the evolution of carbohydrate-binding proteins that use a reactive unnatural amino acid "warhead" and demonstrates that a "synthetic" genetic code can confer a selective advantage by increasing the number of functional groups available to evolution.