Structural evolution and functional adaptation of energy-storage polysaccharides in animals, plants and fungi

Glycogen and starch are the main energy-storage polysaccharides in living organisms, and their structural characteristics directly affect metabolic and mobilization capabilities. This study compared the molecular structural parameters of plant amylopectin, fungal glycogen and animal glycogen (the three "kingdoms" of living organisms), using structural parameterization through biosynthesis-based models. Analysis of the branch density and of the chain-length distribution showed that plant amylopectin branches are sparse, which is optimal for long-term (slow) energy storage. The average degrees of polymerization of fungal glycogen are intermediate between those of plants and animals, and the proportion of short chains is high, which is conducive to rapid energy release. Animal glycogen has high branch density and a high proportion of short chains, supporting rapid and continuous energy supply, consistent with the need for mobility. This analysis shows that the structures of the glucose-storage polymers reflect the organisms' ecological adaptation. This explains the evolutionary optimization relationship between the structural parameters of polysaccharides and energy-storage requirements, and provides a systematic perspective for understanding the synthesis, metabolism and functions of glucose polysaccharides in different living systems. Hypothesis: The molecular structural parameters of plant amylopectin, animal glycogen and fungal glycogen reflect their fitness for purpose.