Which glycosylation type involves attachment to tryptophan residues?
Among glycosylation classes, attachment via carbon-carbon bond to tryptophan indole ring is chemically distinct and relatively rare. C-mannosylation involves α-D-mannopyranose linked to carbon-2 of indole of tryptophan within consensus W-X-X-W or W-X-X-C motif, catalyzed co-translationally inside ER lumen by multi-pass membrane enzymes DPY19L1 through L4 using dolichol-phosphate-mannose as high-energy donor substrate assembled on ER membrane. Modification increases hydrophobicity locally, stabilizes beta-propeller and thrombospondin type 1 repeat folds found in properdin, F-spondin, mindin, ADAMTS proteases and mucins, influences secretion efficiency and solubility. Unlike N-linked glycan attached to asparagine amide or O-linked via serine hydroxyl, C-linkage resists PNGase and O-glycosidases, providing structural reinforcement rather than bulky hydrophilic decoration. Defects in DPY19L1 cause developmental delay and eye anomalies. Golgi-mediated vesicular transport, actin filament association, mannose trimming for ERAD or direct lysosomal delivery refer to trafficking processes unrelated to tryptophan modification, underscoring C-mannosylation as unique post-translational enzymatic linkage expanding proteome chemical diversity beyond canonical N and O linkages and regulatory importance for signaling. Additional coordination with cellular stress pathways ensures fidelity, prevents aggregation, and links trafficking to growth control and proteostasis maintenance across diverse cell types and developmental stages.
Ref: Buettner et al., Mol Cell 72: 2018, C-Mannosylation of Tryptophan by DPY19.