Arabinogalactan Protein and Arabinogalactan: Biomolecules with Biotechnological and Therapeutic Potential

Abstract

Arabinogalactan proteins (AGPs) are high-molecular-weight transmembrane proteoglycans that are implicated in both the vegetative and reproductive stages of plant development. The bulk of an AGP molecule comprises of polysaccharide chains that are mostly anchored to the plasma membrane by glycosyl-phosphatidylinositol. AGP interacts specifically with a class of phenylazoglycoside dyes known as Yariv reagents; these dyes are thus used as histochemical probes to monitor the subcellular localization of AGPs in plant tissues. Arabinogalactans (AGs), a class of polysaccharides, have been reported to be present in a wide range of plant taxa and are prevalent in larch trees. Commercially, larch arabinogalactan (LAG) is used as dietary fiber and prebiotics, as well as in treatment of intestinal disorders. It also has the ability to enhance the activity of the human immune system by stimulating the cytotoxic activity of natural killer (NK) cells via the cytokine network against certain tumor cell lines. Ukonan C, an AG present in the rhizome of Curcuma longa , has the ability to activate reticuloendothelial cells; such stimulated cells with enhanced phagocytic activity can protect the human system from pathogenic foreign agents. Thus, AG acts as a strong activator for two cell types involved in the immune system, namely macrophages and NK cells. In addition, LAG has the ability to block the metastasis of liver tumor cells. Because of its numerous activities, LAG is being used as one of the nonconventional therapeutic agents for cancer treatment. On the other hand, AGPs are of considerable current interest due to their involvement in virtually all facets of plant development. In vitro studies have shown that AGPs play an important role in somatic embryogenesis, which suggests that AGP exhibits plant growth-hormone-like activity. The abiotic stress-protective role of AGP has also been demonstrated. Tissue- and organ-specific expression patterns have already been elucidated for this class of biomolecules, indicating that a specific AGP could be used as a marker for cellular differentiation and as a fate determinant of cultured cells during in vitro differentiation. Due to its immense potentiality, it is considered to be a promising biomolecule, which could resolve several of the hurdles that generally delay the process of crop improvement through biotechnological approaches.