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Programmed cell death protein 1 (PD-1) and programmed cell death ligand 1 (PD-L1) are key targets for cancer therapy. Here, we use automated fast-flow peptide synthesis (AFPS) to rapidly produce these challenging β-sheet-rich proteins in their active forms following oxidative refolding protocols. The methods presented here provide rapid access to synthetic, air-stable mutants of PD-1 and PD-L1 in which L-methionine residues are substituted with L-norleucine, potentially enabling investigation of post-translational modifications and mirror-image analogs for drug discovery.