Incomplete synthesis of N-glycans in congenital dyserythropoietic anemia type II caused by a defect in the gene encoding alpha-mannosidase II.
Congenital dyserythropoietic anemia type II, or hereditary erythroblastic multinuclearity with a positive acidified-serum-lysis test (HEMPAS), is a genetic anemia in humans inherited by an autosomally recessive mode. The enzyme defect in most HEMPAS patients has previously been proposed as a lowered activity of N-acetylglucosaminyltransferase II, resulting in a lack of polylactosamine on proteins and leading to the accumulation of polylactosaminyl lipids. A recent HEMPAS case, G.C., has now been analyzed by cell-surface labeling, fast-atom-bombardment mass spectrometry of glycopeptides, and activity assay of glycosylation enzymes. Significantly decreased glycosylation of polylactosaminoglycan proteins and incompletely processed asparagine-linked oligosaccharides were detected in the erythrocyte membranes of G.C. In contrast to the earlier studied HEMPAS cases, G.C. cells are normal in N-acetylglucosaminyltransferase II activity but are low in alpha-mannosidase II (alpha-ManII) activity. Northern (RNA) analysis of poly(A)+ mRNA from normal, G.C., and other unrelated HEMPAS cells all showed double bands at the 7.6-kilobase position, detected by an alpha-ManII cDNA probe, but expression of these bands in G.C. cells was substantially reduced (less than 10% of normal). In Southern analysis of G.C. and normal genomic DNA, the restriction fragment patterns detected by the alpha-ManII cDNA probe were indistinguishable. These results suggest that G.C. cells contain a mutation in alpha-ManII-encoding gene that results in inefficient expression of alpha-ManII mRNA, either through reduced transcription or message instability. This report demonstrates that HEMPAS is caused by a defective gene encoding an enzyme necessary for the synthesis of asparagine-linked oligosaccharides.
Fukuda
M N
MN
La Jolla Cancer Research Foundation, CA 92037.
Masri
K A
KA
Dell
A
A
Luzzatto
L
L
Moremen
K W
KW
D000742:Anemia, Dyserythropoietic, Congenital / Q000097:blood / Q000201:enzymology / Q000235:genetics*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002462:Cell Membrane / Q000201:enzymology; D015342:DNA Probes; D005796:Genes; D006020:Glycopeptides / Q000302:isolation & purification; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes / Q000201:enzymology; D008361:Mannosidases / Q000097:blood / Q000172:deficiency / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D009844:Oligosaccharides / Q000138:chemical synthesis; D011134:Polysaccharides / Q000096:biosynthesis*; D016339:Spectrometry, Mass, Fast Atom Bombardment
D015342:DNA Probes; D006020:Glycopeptides; D009844:Oligosaccharides; D011134:Polysaccharides; D008361:Mannosidases; C038829:mannosyl-oligosaccharide 1,3 - 1,6-alpha-mannosidase