Atto647N-LPETGG is the sortase sequence, LPETGG, coupled to the fluorescent label Atto647N. Atto647N-LPETGG can be used for site-specific labeling of target proteins using sortase-catalyzed transpeptidation. In this process, sortase A cleaves between the thr and gly residues, forming a thioester intermediate with the peptide probe. A protein N-terminally engineered with a series of glycine residues resolves this intermediate, regenerating the active site cysteine of sortase and conjugating the probe to the N-terminus of the protein. Atto647N-LPETGG contains the Atto647N fluorescent label which is efficiently excited in the range 625 - 660 nm, with strong absorption, high fluorescence quantum yield and high photo-stability.