- A polysaccharide-protein complex (PPC) is a natural or engineered biomacromolecular assembly composed of carbohydrate polymers (polysaccharides) bound to protein chains.
- These complexes can be covalently linked, such as in glycoproteins where carbohydrate moieties are attached directly to amino acid residues, or non-covalently associated through hydrogen bonding, ionic interactions, or hydrophobic forces. Their dual composition gives them distinctive physicochemical properties—polysaccharides contribute structural stability, solubility, and recognition motifs, while proteins provide catalytic, structural, or regulatory functions. This hybrid nature makes polysaccharide-protein complexes highly versatile in biological systems and valuable in biomedical and industrial applications.
- In nature, PPCs are abundant across different organisms. In plants and fungi, they often serve structural or protective roles, with the protein portion enhancing the functional diversity of the polysaccharide. In bacteria, polysaccharide-protein complexes form critical elements of the cell envelope, including capsules and surface glycoproteins, which aid in adhesion, immune evasion, and environmental resilience. In animals, they appear as glycoproteins such as mucins, antibodies, and proteoglycans, where the polysaccharide moiety provides hydration, structural support, or cell signaling functions. Thus, PPCs are not only structural but also play central roles in cell recognition, immune regulation, and intercellular communication.
- One of the most studied classes of PPCs are those derived from medicinal mushrooms and fungi, where they act as potent biological response modifiers (BRMs). Famous examples include PSK (polysaccharide-K, also called krestin) and PSP (polysaccharide-peptide) from Trametes versicolor, as well as complexes found in Ganoderma lucidum (reishi mushroom). These fungal PPCs typically consist of β-(1→3)-glucans with β-(1→6) branching linked to proteins, which stabilize the polysaccharide’s triple-helical conformation and improve solubility. Biologically, they are known for their immunomodulatory and antitumor effects, acting primarily by stimulating macrophages, dendritic cells, T lymphocytes, and natural killer (NK) cells. By binding to receptors such as Dectin-1, TLRs, and complement receptors, they enhance cytokine secretion and immune surveillance, indirectly inhibiting tumor progression and supporting host defense against infections.
- Clinically, mushroom-derived polysaccharide-protein complexes have been developed into approved anticancer adjuvants in some countries. For example, PSK is used in Japan as part of standard therapy for gastric, colorectal, and lung cancers, where it helps reduce side effects of chemotherapy and prolong survival. PSP is similarly studied in China for its immune-supportive properties. Beyond oncology, PPCs have demonstrated antiviral, antibacterial, antioxidant, and hepatoprotective activities, as well as beneficial effects on cholesterol metabolism and blood glucose regulation, making them promising for chronic disease management.
- From a biochemical standpoint, the structure–function relationship of PPCs is crucial. The polysaccharide’s backbone type, degree of branching, and molecular weight significantly influence immune activation, while the protein fraction enhances solubility, receptor binding, and biological stability. This synergy explains why polysaccharide-protein complexes often display greater bioactivity than polysaccharides or proteins alone.
- In addition to their medicinal applications, PPCs have industrial significance. In the food industry, they act as natural emulsifiers, stabilizers, and texturizers because of their amphiphilic nature. In biotechnology, they are explored for use in drug delivery systems, vaccines, and biomaterials, as their biocompatibility and immunological properties make them highly adaptable platforms.
