Site-selective lysine modification of native proteins and peptides via kinetically controlled labeling

The site-selective modification of the proteins RNase A, lysozyme C, and the peptide hormone somatostatin is presented via a kinetically controlled labeling approach. A single lysine residue on the surface of these biomolecules reacts with an activated biotinylation reagent at mild conditions, physiological pH, and at RT in a high yield of over 90%. In addition, fast reaction speed, quick and easy purification, as well as low reaction temperatures are particularly attractive for labeling sensitive peptides and proteins. Furthermore, the multifunctional bioorthogonal bioconjugation reagent (19) has been achieved allowing the site-selective incorporation of a single ethynyl group. The introduced ethynyl group is accessible for, e.g., click chemistry as demonstrated by the reaction of RNase A with azidocoumarin. The approach reported herein is fast, less labor-intensive and minimizes the risk for protein misfolding. Kinetically controlled labeling offers a high potential for addressing a broad range of native proteins and peptides in a site-selective fashion and complements the portfolio of recombinant techniques or chemoenzymatic approaches.