Boiling Licorice Produces Self-assembled Protein Nanoparticles: A Novel Source of Bioactive Nanomaterials

As a popular ingredient for western and traditional Chinese medicine, the root and rhizome of Chinese licorice (Glycyrrhiza uralensis Fisch.) is often administered in the form of decoction. The protein nanoparticles (NPs) self-assembled during the process of decoction. A major constitutive protein (GLP) was purified and determined to have a molecular weight of 28kDa with N-terminal sequence of NPDGL IACYC GQYCW. Over 80% of the purified GLP self-assembled into spherical NPs with diameters of 74.1±0.7 nm and ζ-potential of -24.3±1.7 mV when it was boiled in Tris-HCl buffer (pH=7.9, 20 mM) at 100℃ for 60 min. Each nanoparticle was estimated by SEC-MALLS approach to be composed of approximately 23 protein molecules. The NPs and GLP showed low cellular toxicity upon four types of cells including MDCK, L-02, HepG2 and Caco2 cells, while the NPs promoted proliferation of normal hepatocytes by 67%. The NPs solubilized the insoluble astragaloside IV by encapsulation. Results suggest a great potential for GLP-NPs as a promising prototype of drug vehicle, a novel source of bioactive nanomaterials from herbal proteins, as well as a new mode of function with herbal components.