This C-terminal Sortagging peptide acts as a (oligo)glycine nucleophile in the final steps of a sortagging protein labelling reaction. This reaction results in the (AF647) fluorescent moiety being attached to the C-terminus of the target protein or peptide.

Sortase A (SrtA) from Staphylococcus aureus has become a valuable tool via sortase-mediated ligation of various substrates for bioconjugation. SrtA recognises the LPxTG motif as a substrate. Cleavage results in a thioester intermediate between the peptide and SrtA. The thioester is resolved by the N-terminus of a nucleophile, usually with two glycines at the start, creating a new bond. In bacteria, SrtA aids surface proteins being ligated into the peptidoglycan cross-bridge. The peptidoglycan of S. pyogenes provides an N-terminal alanine residue for the ligation reaction. AAA-C(AF647) is a nucleophile for SrtA S. pyogenes; the sortase-mediated ligation reaction results in protein labelling with a C-terminal Alexa Fluor® 647 fluorescent dye. Alexa Fluor® 647 has a maximum emission of 668 nm when excited at 650nm. AAA-C(AF647) has the potential to be used for a wide variety of purposes, as has been demonstrated with other SrtA ligations such as intracellular ligation of protein in living cells.