Reactions that can selectively modify amino acid sequences within peptides and proteins are important for preparing protein reagents, immobilizing proteins, and making antibody-drug conjugates. The development of new reactions often begins with known chemistries and optimizes yields using a small set of peptide reactants. This article describes the use of peptide arrays and self-assembled monolayers for matrix-assisted laser desorption/ionization mass spectrometry (SAMDI-MS) to discover and characterize unanticipated sequence-selective reactions of peptides. This work reports the selective acetylation of HY (histidine-tyrosine) and YH (tyrosine-histidine) dyads when treated with acetic anhydride in aqueous conditions. More broadly, this example illustrates the benefits of using peptide arrays and a label-free analysis method to discover peptide-modifying reactions and gain mechanistic insight into their sequence specificity.
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