Chemical Synthesis of Mirror-image Proteins and Their Application to Drug Discovery

Mirror-image proteins (D-proteins) comprise D-amino acids and achiral glycine, which are capable of assembling into mirror-image architectures of native L-proteins. Although D-proteins cannot be obtained through recombinant technology, synthetic proteins with more than 100 residues have been prepared using advanced peptide chemistry techniques, including solid-phase peptide synthesis and native chemical ligation. To date, a number of mirror-image versions of target proteins have been synthesized and used to screen the therapeutic potential of mirror-image peptides (D-peptides), nucleic acids (L-nucleic acids), and natural products (mirror-image enantiomers). We have been exploring the looking-glass world to expand the repertoire of protein-based therapeutics through mirror-image screening. To this end, we have established processes for synthesizing nanobodies (VHH antibodies) and monobodies, which contain three variable regions on stable scaffolds to bind epitopes on target proteins. Despite their identical sequences, the mirror-image forms of nanobodies and monobodies are significantly less immunogenic in mice than their L-form counterparts. Scaffolds of mirror-image proteins have also been chemically modified to study their pharmacokinetic properties and potential for bioconjugation.