Although conjugation with polyethylene glycol (PEGylation) improves the pharmacokinetics of therapeutic proteins, it drastically decreases their bioactivity. Site-specific PEGylation counters the reduction in bioactivity, but developing PEGylated proteins with equivalent bioactivity to that of their unmodified counterparts remains challenging. This study aimed to generate PEGylated proteins with equivalent bioactivity to that of unmodified counterparts. Using interferon (IFN) as a model protein, a highly bioactive Lys-deficient protein variant generated using our unique directed evolution methods enables the design of a site-specific di-PEGylated protein. Antiviral activity of our di-PEGylated IFN was similar to that of unmodified IFN-α2b. The di-PEGylated IFN exhibited 3.0-fold greater antiviral activity than that of a commercial PEGylated IFN. Moreover, our di-PEGylated IFN showed higher in vitro and in vivo stability than those of unmodified IFN-α2b. Hence, we propose that highly bioactive Lys-deficient proteins solve the limitation of conventional PEGylation with respect to the reduction in bioactivity of PEGylated proteins.
Keywords: Lys-deficient proteins; directed evolution; genetic code engineering; interferon; site-specific di-PEGylation.