ABSTRACT
Living organisms on this earth have evolved to use carbohydrates for most of their biological processes, such as energy source for survival, structural framework, and biological functions. Glycans have many biochemical, structural, and functional features that make them ideal to be universally used by living cells in energy metabolism, cellular interactions, and the formation of protective physical barriers against the outside environment. The glycans being ubiquitous constituents of all the cell surfaces and the surrounding cellular environments, are not only important for the biological processes of the host but also for the binding of pathogens to them. Pathogens are in constant contact with their host, and overtime have co-evolved traits to explore the host glycans for their survival as well as pathogenesis. Pathogens belonging to diverse dimensions of life like bacteria, fungi, helminths, protozoans, and viruses use different types of glycans like negatively charged sialic acid, oligomannose glycans, and glycosaminoglycans (GAGs) to establish host-pathogen relations. The enormous diversity, abundance, and density of the host glycans are subjected to tremendous immune selection pressure to evade the constantly targeting and more rapidly evolving pathogens that infect them. This immense selection pressure leads to development of diverse glycan expression patterns on the host cells without compromising their own survival. This may attribute to the significant structural variation 158of glycans in nature, which add to biological diversity and to speciation as well. Furthermore, the glycans also play a critical role in antigenicity and virulence in these host-pathogen interactions and are therefore considered as potential drug targets.
