Enzyme-mediated site-specific antibody-protein modification using a ZZ domain as a linker

A ZZ domain (ZZ) and alkaline phosphatase (AP), luciferase (Luc), or glucose oxidase (GOD) were conjugated using Sortase A (SrtA) from Staphylococcus aureus. The specific peptidyl linker for SrtA was genetically fused to the C-terminus of ZZ, and the other linker was fused to the N-terminus of AP, Luc, or GOD, respectively. The resultant proteins were obtained separately by bacterial expression. The recombinant peptide-tagged ZZ and AP, Luc, or GOD were site-specifically conjugated by SrtA through the extra peptidyl linkers in vitro. The SrtA reaction had little influence on either the antibody-binding activity of the ZZ moiety or the enzymatic activity of AP, Luc, or GOD moieties of the conjugates. Additionally, antibody-ZZ-proteins were yielded easily by mixing antibody with ZZ-AP, ZZ-Luc, or ZZ-GOD, allowing their use in an enzyme-linked immunosorbent assay. These results suggest that the enzymatic approach with SrtA facilitates the construction of ZZ-proteins. Furthermore, mixing antibody and ZZ-proteins produces a wide variety of antibody-ZZ-proteins.