Bioaffinity Recovery of Linear CRGDS Peptides Grafted to Zwitterionic PAMAM Nanocarriers

Functional oligopeptides derived from natural proteins are often used as targeting groups or therapeutic drugs but always suffer from a dramatic bioaffinity decrease due to the loss of conformational restriction in proteins, which increases their entropy state. It is worth noting that the linear Cys-Arg-Gly-Asp-Ser (CRGDS) oligopeptide can spontaneously restore its natural conformation by anchoring one terminus and forming hydrogen bonds on another terminus, on protein-like zwitterionic fifth-generation polyamide-amine (G5 PAMAM) nanocarriers, thus exhibiting high bioaffinity. However, the different physicochemical properties of nanocarriers have an impact on the bioaffinity recovery of linear CRGDS. In this work, it is found that the bioaffinity decreases with the reduction of generation of PAMAM and zwitterionic G3 PAMAM is a turning point for bioaffinity recovery via a series of in vitro experiments. This indicates that the spontaneous restoration of the native conformation of the RGD segment requires proper surface group density and structural rigidity of the zwitterionic nanocarrier for reducing the entropic energy of CRGDS peptides before binding. This approach paves a way for functional reproduction of protein molecules using low-cost synthetic polymers for extensive biomedical applications.