Selective Coupling of Click Anchors to Proteins via Trypsiligase

The combination of pure chemical methods with enzymatic approaches offers a kit system with maximum flexibility for site-specifically tagging proteins with a broad variety of artificial structures. Trypsiligase, a recently introduced designer enzyme for both N- and C-terminal site-specific labeling of peptides and proteins, has been used to introduce click anchors into the human protein cyclophilin 18 and the antibody Fab fragments anti-TNF alpha and anti-Her2. The subsequent click reactions with tetrazine or norbornene moieties lead to quantitative conversions to the corresponding dihydropyridazine products, thereby forming a stable covalent linkage between the label and the protein of interest. With this technology, cyclophilin 18 has been efficiently modified with the fluorescent dansyl moiety and the pharmaceutically relevant polymer PEG exclusively at its N-terminus. With the same methodology, the Fab fragments of anti-TNF alpha and anti-Her2 were derivatized exclusively at their C-terminal ends with PEG and the fluorescent dye carboxyfluorescein in the case of anti-TNF alpha or with the cytotoxic payload DM1 in the case of anti-Her2, to form a homogeneous antibody-drug conjugate (ADC).