Enzymes have become an attractive option for protein modification chemistry due to the remarkable site-specificity they afford. Of particular interest is sortase A from taphylococcus aureus (SrtAaur), which has garnered attention for its ability to install a variety of non-natural modifications to a conserved oligopeptide substrate. In addition to SrtAaur it has become apparent that sortase A homologs exist in other bacterial strains, each of which is potentially a novel catalyst for protein engineering. Previous work has demonstrated that eight representative sortase A homologs exhibit unique specificities for synthetic peptide substrates, capable of identifying characteristic combinations of amino acids in the “sorting motif.” Presented here is a nucleophile profile of the most promiscuous sortase A homolog investigated, that from Streptococcus pneumoniae (SrtApneu). Exhibiting unique specificities, this SrtA variant may enable unique protein modification chemistry
