Optimization of Protein Isolation and Label–free Quantitative Proteomic Analysis in Four Different Tissues of Korean Ginseng

Korean ginseng is one of the most valuable medicinal plants worldwide. Yet, our understanding of ginseng proteomics is largely limited due to difficulties in extraction and resolution of ginseng proteins because of the presence of natural contaminants such as polysaccharides, phenols, and glycosides. Here, we compared four different protein extraction methods, namely, TCA/acetone, TCA/acetone–MeOH/chloroform, Phenol–TCA/acetone, and Phenol–MeOH/chloroform methods. Consequently, the TCA/acetone–MeOH/chloroform method displayed the highest extraction efficiency, thus it was used for the comparative proteome profiling of leaf, root, shoot, and fruit by a label–free quantitative proteomics approach. This approach led to the identification of 2,604 significantly modulated proteins among four tissues. We could pinpoint differential pathways and proteins associated with ginsenoside biosynthesis including the methylerythritol 4–phosphate (MEP) pathway, the mevalonate (MVA) pathway, UDP–glycosyltransferases (UGTs), and oxidoreductases (CYP450s). The current study reports an efficient and reproducible method for the isolation of proteins from a wide range of ginseng tissues and provides a detailed organ–based proteome map and a more comprehensive view of enzymatic alterations in ginsenoside biosynthesis.