Sortase is a family of transpeptidases found in Gram-positive bacteria, which is divided into two subfamilies: Sortase A and Sortase B. Its main function is to catalyze the covalent attachment of cell surface proteins to the cell wall. Among them, Sortase A （SrtA） has been studied more extensively. Sortase A （SrtA） can specifically recognize proteins with a C-terminal conserved amino acid sequence LPXTG and an N-terminal polyglutamine （X is any amino acid except cysteine and tryptophan）.