Exploring marine glycans: structure, function, and the frontier of chemical synthesis.

Marine glycans are structurally diverse biomolecules that play pivotal roles in oceanic carbon cycling by regulating microbial metabolism, accelerating organic matter turnover, and contribute to carbon sequestration. Glycans originating from marine organisms exhibit a wide range of bioactivities and applications in medicine, biotechnology, cosmetics, food and agriculture. The structural complexity of glycans poses significant challenges in understanding their functions, as traditional purification and characterization methods are often hindered by their inherent heterogeneity. To overcome these challenges, enzymatic extraction using glycoside hydrolases and carbohydrate-active enzymes (CAZymes) enables the selective recovery of native glycans, while automated glycan assembly (AGA) provides a robust approach for the rapid and reproducible synthesis of structurally defined glycans. Subjecting synthetic glycans to enzymatic degradation enables researchers to explore the inverse relationship between glycan complexity and microbial degradation, suggesting that algae can generate complex glycans at a rate exceeding bacterial decomposition, thereby reinforcing carbon storage. Here, we present a comprehensive overview of marine glycan sources and their structural diversity. We highlight the importance of employing two complementary methods, enzymatic extraction as a critical tool for glycan identification and AGA as an advanced synthetic platform, to build a refined framework for elucidating the ecological role and industrial potential of marine glycans.