Phosphoglycans

Phosphoglycans are a class of glycoconjugates in which carbohydrate chains include covalently bound phosphate groups as part of the polymer, typically forming phosphodiester linkages between sugar residues. This phosphate-containing geometry distinguishes phosphoglycans from other glycans whose linkages are solely glycosidic. The presence of phosphate confers negative charge to the molecule and can influence hydration, conformation, and interactions with proteins.

Structurally, phosphoglycans may consist of repeating sugar units or more complex branched architectures. In some cases, the glycan chain is attached to a lipid or protein anchor, forming lipophosphoglycans or proteophosphoglycans, respectively. A prominent example occurs in certain kinetoplastid parasites, such as Leishmania and Trypanosoma, where lipophosphoglycan (LPG) and related phosphoglycans populate the cell surface. These molecules often feature phosphoglycan repeating units linked to a GPI anchor or to a protein core, and they can vary with life stage or species.

Occurrence and function vary by organism. In parasites, phosphoglycans are implicated in surface protection, adhesion, immune evasion, and interaction with host tissues. In bacteria and plants, phosphorylated polysaccharides can contribute to capsule structure, surface charge, and interactions with the environment. The biosynthesis of phosphoglycans involves specialized enzymes that form phosphodiester bonds and incorporate sugar residues, while degradation requires phosphodiesterases and glycosidases. Analytical characterization typically employs nuclear magnetic resonance, mass spectrometry, and phosphate-detection methods to determine linkage types, repeating-unit composition, and the extent of phosphorylation.