The covalent attachment of chemical groups to proteins is a critically important tool for the study of protein function and the creation of protein-based materials. Methods of site-specific protein modification are necessary for the generation of well-defined bioconjugates possessing a new functional group in a single position in the amino acid sequence. This paper describes a pyridoxal 5′-phosphate (PLP) mediated transamination reaction that is specific for the N-terminus of a protein. The reaction oxidizes the N-terminal amine to a ketone or an aldehyde, which can form a stable oxime linkage with an alkoxyamine reagent of choice. Screening studies have identified the most reactive N-terminal residues, facilitating the use of site-directed mutagenesis to achieve high levels of conversion. Additionally, this reaction has been shown to work on a number of targets that are not easily accessed through heterologous expression, such as monoclonal antibodies.
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