An AviTag/BirA Platform for IL7: Minimized Activity Loss over Random Biotinylation

Interleukin-7 (IL7) plays a pivotal role in T cell biology; however, its therapeutic potential is constrained by its short half-life. Conventional chemical biotinylation frequently results in random modifications that compromise its bioactivity. This study endeavors to establish a prokaryotic system for the site-specific biotinylation of IL7 utilizing AviTag and underscores its advantages over random biotinylation in retaining functionality. A recombinant plasmid (pET-Dual-His-IL7-avi-birA) was constructed to coexpress AviTag-fused IL7 and BirA ligase, which was subsequently transformed into Escherichia coli BL21-(DE3). Optimal expression conditions were determined as follows: cultivation at 37 °C with shaking at 200 rpm for 12 h following induction with 0.5 mM IPTG in the presence of 80 μM biotin. The expressed protein, predominantly localized in inclusion bodies, was purified using Ni-NTA resin supplemented with 250 mM imidazole. Biotinylation efficiency was confirmed through Western blot analysis and native polyacrylamide gel electrophoresis (PAGE). Functional characterization encompassed T cell proliferation and apoptosis assays employing CCK-8 methodology and flow cytometry, respectively, alongside comparative analyses against chemically randomized biotinylated IL7. Site-specifically biotinylated IL7 (biotin-IL7) was successfully generated and purified. It specifically bound streptavidin and retained T cell proliferative activity comparable to native IL7. Compared with randomly biotinylated IL7, site-specific exhibited stronger induction of T cell proliferation, less interference with antibody binding, and more effective downregulation of T cell apoptosis. The AviTag/BirA-based biotinylation system provides an efficient, economical, and scalable method for producing functional biotin-IL7 with enhanced stability and targeting potential. The key advantages of site-specific over random biotinylation were confirmed: preservation of IL7's bioactivity, reduction of functional interference, and enhancement of therapeutic efficacy. This approach offers a paradigm for optimizing small therapeutic proteins, particularly in cancer immunotherapy, while highlighting the need to improve soluble expression and biotinylation efficiency.