High-resolution mastigoneme structure reveals 5’,5’-phosphodiesters stabilized glycan folding

Abstract Glycans play a crucial role in structure organization, energy metabolism, and signal transduction in living organisms. Compared with proteins and nucleic acids, glycans exhibit remarkable molecular heterogeneity, extensive conformational flexibility, and diverse linkages. These properties pose significant challenges for obtaining high-resolution structure of glycans. Here, we report a cryo-EM structure of the heavily glycosylated Chlamydomonas mastigoneme at 2.3-2.5 Å resolutions. In addition to enabling analysis of accurate interactions for glycosyl packing, the high resolution map reveals an unprecedented 5’,5’-phosphodiester bond that links adjacent glycan chains attached to hydroxyproline (Hyp) residues n and n+3. Structural analysis reveals a secondary structural element for glycoconjugates, which we name the poly-Hyp (pHP) glycohelix. Our work represents an important advancement in deciphering glycan folding.