Access to Faster Eukaryotic Cell Labeling with Encoded Tetrazine Amino Acids.

Labeling of biomolecules in live eukaryotic cells has been limited by low component stability and slow reaction rates. We show that genetically encoded tetrazine amino acids in proteins reach reaction rates of 8 × 10 M s with sTCO reagents, making them the fastest site-specific bioorthogonal labels in eukaryotic systems. We demonstrate that tetrazine amino acids are stable on proteins and are capable of quantitative labeling with sTCO reagents.