Asparaginyl Ligases: New Enzymes for the Protein Engineer's Toolbox

Enzyme‐catalysed site‐specific protein modifications enable the precision manufacture of conjugates for the study of protein function and/or for therapeutic or diagnostic applications. Asparaginyl ligases are a class of highly efficient transpeptidases with the capacity to modify proteins bearing only a tripeptide recognition motif. Herein, we review the types of protein modification that are accessible using these enzymes, including N‐ and C‐terminal protein labelling, head‐to‐tail cyclisation, and protein‐protein conjugation. We describe the progress that has been made to engineer highly efficient ligases as well as efforts to chemically manipulate the enzyme reaction to favour product formation. These enzymes are powerful additions to the protein engineer‘s toolbox. Intents and (re)purposes: Asparaginyl ligases are highly efficient transpeptidases. These enzymes naturally catalyse the head‐to‐tail cyclisation of small plant peptides, but recently have been repurposed for the modification of diverse proteins. This minireview describes the current state of protein engineering with asparaginyl ligases.