Effects of Individual Amino Acids on the Blood Circulation of Biosynthetic Protein Nanocages: Toward Guidance on Surface Engineering

Protein nanocages (PNCs) hold great promise for developing multifunctional nanomedicines. Long blood circulation is a key requirement of PNCs for most in vivo application scenarios. In addition to the classical PEGylation strategy, short peptides with a specific sequence screened via phage display are also very effective in prolonging the blood half-life (t ) of PNCs. However, there is a lack of knowledge on how individual amino acids affect the circulation of PNCs. Here the effects of the 20 proteinogenic amino acids in the form of an X or X tag (X represents an amino acid) are explored on the pharmacokinetics of PNCs, which lead to the formation of a heatmap illustrating the extent of t prolongation by each proteinogenic amino acid. Significantly, oligo-lysine and oligo-arginine can effectively prolong the t of strongly negatively charged PNCs through charge neutralization, while oligo-cysteine can also do so, but via a different mechanism, mediating the covalent binding of PNCs with plasma albumin as a stealth material. These findings are extendible and offer guidance for surface-engineering biosynthetic PNCs and other nanoparticles.