title: Enzymes that recognize dolichols participate in three glycosylation pathways and are required for protein secretion.
abstract: We have explored the structure, function, and membrane topography of enzymes that recognize dolichols and participate in glycosylation pathways in the endoplasmic reticulum. Enzymes that interact with dolichols, including dolichyl phosphate mannose (Dol-P-Man) synthase and UDP-GlcNAc:Dol-P-transferase, revealed a conserved amino acid sequence in membrane-spanning regions. The consensus is Phe-Ile/Val-Xaa-Phe/Try-Xaa-Xaa-Ile-Pro-Phe-Xaa-Phe/Tyr, and we propose it is involved in dolichol recognition. We have used yeast mutants to demonstrate the role of dolichols in three glycosylation pathways. At its nonpermissive temperature, a Dol-P-Man synthase mutant (dpm1) was blocked in N-glycosylation, O-mannosylation, and glycosyl phosphoinositol membrane anchoring of protein, most likely because Dol-P-Man serves as mannosyl donor in all three pathways. The secretion mutant sec59 has a similar phenotype to dpm1, and the presence of a dolichol recognition sequence in the SEC59 protein gave a clue to its defect, which is in dolichol kinase. Comparison of yeast glycosylation mutant suggests that the ability to carry out N-glycosylation alone is sufficient to allow yeast to secrete glycoproteins and that an N-linked saccharide of a minimum size must be attached to proteins for cells to be able to secrete them and maintain a functional secretory pathway.
authors.affiliation: Department of Biochemistry, University of Illinois, Urbana-Champaign 61801.
authors.forename: P
authors.initials: P
authors.lastname: Orlean
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002240:Carbohydrate Sequence; D016384:Consensus Sequence; D006224:Cricetinae; D004288:Dolichol Phosphates / Q000378:metabolism*; D004286:Dolichols / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal; D006023:Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D006031:Glycosylation; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D008322:Mammals / Q000235:genetics / Q000378:metabolism; D008364:Mannosyltransferases / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D017855:Transferases (Other Substituted Phosphate Groups)
chemical_list: D004288:Dolichol Phosphates; D004286:Dolichols; D005656:Fungal Proteins; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D016695:Glycosyltransferases; D008364:Mannosyltransferases; C035777:chitobiosyldiphosphodolichol beta-mannosyltransferase; C022755:dolichyl-phosphate beta-D-mannosyltransferase; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); C023222:UDPacetylglucosamine-dolichyl-phosphate acetylglucosamine-1-phosphate transferase