Selective modification of biomolecules provides scientists with an effective tool for a multitude of bioanalytical, therapeutic, biological and bioengineering applications. However, chemical strategies that can target a particular functional group at a single site in the presence of reactive amino acid side chains on protein surfaces are limited. We have developed a multicomponent bioconjugation approach for selective labeling of proteins containing secondary amines. This method does not require any genetic engineering of the protein target and protection of the side chains of other amino acids. The resulting bioconjugation reaction leads to the formation of a highly stable C-C bond at the site of the conjugation. The broad utility of the bioconjugation reaction is demonstrated by conjugation of various probes such as dye, peptides, and PEG on different proteins containing a proline at the N-terminus such as creatine kinase and aldolase. This method is employed for labeling monomethyl lysine containing posttranslational modifications (PTMs) on proteins with various cargoes. The dysregulation of monomethyl lysine PTMs has been linked to a variety of different biological malfunctions, yet the chemical methods for selective detection of mono methyl lysine PTMs are still lacking. This selective tagging methodology can effectively detect monomethyl lysine PTMs thus has a potential to further our understanding of the role of monomethylated lysine containing PTMs in regulating various cellular signaling processes.