Sortase domain found in subfamily 1 of the class D family of sortases
Class D sortases are cysteine transpeptidases distributed in Gram-positive bacteria (mainly present in Firmicutes). The prototypical subfamily 1 of class D sortase from Bacillus anthracis (named Ba-SrtC) covalently attaches proteins bearing a noncanonical LPNTA sorting signal, such as the BasH and BasI proteins, to the peptidoglycan of the cell wall that facilitate sporulation. BasH is exclusively anchored to the forespore cell wall envelope, while BasI is attached to the diaminopimelic acid moiety of the peptidoglycan of predivisional cells. Ba-SrtC lacks the N-terminal signal peptide and membrane anchor. The family also includes many class D sortase homologs from Gram-negative bacteria, but the functions of these enzymes are unknown.