The present invention relates to a cellular transport system for bringing a sulfonic acid construct which carries a cargo into a cell and releasing the cargo in the cell's cytoplasm, the cellular transport system comprising: (i) a sulfonate transporter located in the cytoplasm membrane of the cell wherein said sulfonate transporter is capable of transporting said sulfonic acid construct across the cytoplasm membrane into the cytoplasm； (ii) a ?-glutamyl transferase (GGT； EC 2.3.2.2) which is modified to be located in the cytoplasm of the cell, wherein said ?-glutamyl transferase is capable of hydrolyzing said sulfonic acid construct so as to release the cargo. Moreover, the present invention relates to the use of a cellular transport system for bringing a sulfonic acid construct which contains a cargo into a cell and releasing the cargo in the cell's cytoplasm. Further, the present invention relates to a ?-glutamyl transferase for hydrolyzing a sulfonic acid construct which contains a cargo.
