A protein-sorting transpeptidase is an enzyme, such as the sortase SrtA[1] of Staphylococcus aureus, that cleaves one or more target proteins produced by the same cell, as part of a specialized pathway of protein targeting.
The typical prokaryotic protein-sorting transpeptidase is characterized as a protease, but does not simply hydrolyze a peptide bond.
Instead, the larger, N-terminal portion of the cleaved polypeptide is transferred onto another molecule, such as a precursor of the peptidoglycan cell wall in Gram-positive bacteria.
Myxosortases, homologs of the type 2 CAAX prenyl protease Rce1, are analogous protein-sorting enzymes, but they are unlikely to function as transpeptidases.
[5] It is likely, instead, that the cysteine residue in the target sequence is modified by a separate enzyme, and that modification is followed by cleavage by the myxosortase, as happens with Rce1.