- A polysaccharide-peptide complex (PSPC) is a type of biomacromolecular conjugate consisting of carbohydrate chains (polysaccharides) covalently or non-covalently linked with peptides or proteins.
- These complexes are widely found in nature, particularly in fungi, bacteria, and certain plants, where they often play structural or protective roles. The combination of sugar residues and peptide backbones provides unique structural and functional properties that differ from those of pure polysaccharides or proteins alone. In many cases, the peptide component stabilizes the polysaccharide conformation, enhances solubility, or modifies its biological activity.
- Biologically, polysaccharide-peptide complexes are best known for their immunomodulatory and antitumor activities. They interact with immune receptors such as Dectin-1, Toll-like receptors (TLRs), and complement receptors on immune cells, stimulating macrophages, T cells, dendritic cells, and natural killer (NK) cells. This results in the production of cytokines, activation of phagocytosis, and enhanced immune surveillance, allowing the host to better resist infections and suppress tumor growth. Unlike cytotoxic drugs, PSPCs generally act by boosting the body’s own immune defenses rather than directly killing tumor cells.
- Several well-studied examples of polysaccharide-peptide complexes come from medicinal mushrooms. The most famous is PSK (polysaccharide-K), also known as krestin, derived from Trametes versicolor (turkey tail mushroom). PSK has been extensively used in Japan as an adjuvant cancer therapy, where it is prescribed alongside chemotherapy or radiotherapy for cancers such as gastric, colorectal, and lung cancers. Another related compound, PSP (polysaccharide-peptide), isolated from the same mushroom, has demonstrated similar immunomodulatory effects and is used in complementary medicine, particularly in China. These mushroom-derived PSPCs typically contain β-glucan backbones with protein or peptide moieties that enhance their stability and bioactivity.
- Beyond oncology, polysaccharide-peptide complexes also exhibit a wide range of pharmacological activities, including antiviral, antibacterial, antioxidant, hepatoprotective, and cholesterol-lowering effects. Their multifunctional properties have made them valuable not only in medicine but also in the development of functional foods and nutraceuticals. In addition, their biocompatibility and biodegradability make PSPCs promising candidates for drug delivery systems, as they can be engineered to carry therapeutic molecules while providing immunological benefits.
- From a biochemical perspective, the structure–function relationship of PSPCs is an active area of research. Factors such as the degree of branching in the polysaccharide, the type of glycosidic linkages, the size of the peptide moiety, and the method of conjugation all influence biological activity. Generally, β-(1→3)-glucan backbones with β-(1→6) branching are strongly associated with immune activation, while the peptide fraction can improve bioavailability or act as a co-factor in receptor recognition.
