This 5-amino acid peptide is a sortase substrate, C-terminal sorting signal. Sortase cleaves surface proteins at the LPXTG motif and catalyzes the formation of an amide bond between the carboxyl group of threonine and the amino group of cell-wall crossbridges. Sortases are a family of Gram-positive transpeptidases responsible for anchoring surface protein virulence factors to the peptidoglycan cell wall layer. Cleavage of this FRET substrate by sortase reveals the fluorescent signal, Abs/Em = 340/490 nm.