Natural Polyphenols Augment Cytosolic Protein Delivery by a Functional Polymer

Cytosolic protein delivery is of great importance for basic cell biology and the discovery of novel protein-based biotherapeutics. It remains a challenging task because of the limited binding sites on proteins and their relatively large size. As a result, most current approaches for cytosolic protein delivery need covalent modification on native proteins, which is usually involved with complicated synthesis, reduced protein bioactivity, and unexpected safety concerns. In this study, we proposed a novel strategy to deliver proteins of different molecular sizes and isoelectric points by specific recognitions between natural polyphenols and boronic acid-containing polymers. Protein molecules were decorated with polyphenols via noncovalent hydrogen-bond/hydrophobic interactions or reversible dynamic covalent bonds. The natural polyphenols increase the binding affinity between proteins and boronic acid-containing polymers, allow the release of bound proteins in acidic environments because of pH-sensitive property of catechol-boronate esters, and thus greatly promote the cytosolic delivery efficiency. This strategy showed robust efficiency in the delivery of various proteins such as bovine serum albumin, phycoerythrin, and ribonuclease A and maintained the protein bioactivity after intracellular release. The reported strategy permits the development of a polyphenol-involved polymer platform for cytosolic protein delivery.