Abnormal cellular physiology Intracellular accumulation of Dol-PP-GlcNAc2Man5 2019-12-14T09:45:01Z Intracellular accumulation of the lipid-linked oligosaccharide intermediate Man5GlcNAc2-PP-dolichol. Intracellular accumulation of Dol-PP-GlcNAc2Man5 can result from a defect in ALG3, which encodes a mannosyltransferase that transfers mannose from dolichyl phosphate mannose. The accumulation can be measured in fibroblasts. During protein N-glycosylation, glycans from lipid-linked oligosaccharides (LLOs) are transferred onto asparagine residues located in N-glycosylation sequons. The synthesis of LLO comprises three steps: It begins with the biosynthesis of the intermediate Dol-PP-GlcNAc2Man5, which occurs on the cytoplasmic side of the endoplasmic reticulum (ER). The second step is the flipping of this intermediate to the luminal side of the ER. The third step comprises the glycan extension in the ER lumen, yielding Dol-PP-GlcNAc2Man9.