Optimized Production of Fc Fusion Proteins by Sortase Enzymatic Ligation

Fc fusions are a growing class of drugs comprising an antibody Fc domain covalently linked to a protein or peptide and can pose manufacturing challenges. In this study we evaluated three synthetic approaches to generate Fc fusions, using Fc-insulin as a model drug candidate. Engineered human IgG1 was digested with HRV3C to produce an Fc fragment with a C-terminal sortase tag (Fc-LPETGGH6). The synthesis of Fc-insulin2 from Fc-LPETGGH6 was evaluated with direct sortase-mediated ligation (SML) and two chemoenzymatic strategies. Direct SML was performed with triglycine-insulin, and chemoenzymatic strategies used SML to fuse either triglycine-azide or triglycine-DBCO prior to linking insulin with copper-catalyzed or strain-promoted azide-alkyne cycloaddition. Reaction conditions were optimized by evaluating reagent concentrations, relative equivalents, temperature, and time. Direct SML provided the most effective reaction yields, converting 60–70% of Fc-LPETGGH6 to Fc-insulin2, whereas our optimized chemoenzymatic synthesis converted 30–40% of Fc-LPETGGH6 to Fc-insulin2. Here we show that SML is a practical and efficient method to synthesize Fc fusions and provide an optimized pathway for fusion drug synthesis.