A new type of congenital disorders of glycosylation (CDG-Ii) provides new insights into the early steps of dolichol-linked oligosaccharide biosynthesis.
Deficiency of GDP-Man:Man1GlcNAc2-PP-dolichol mannosyltransferase (hALG2), is the cause of a new type of congenital disorders of glycosylation (CDG) designated CDG-Ii. The patient presented normal at birth but developed in the 1st year of life a multisystemic disorder with mental retardation, seizures, coloboma of the iris, hypomyelination, hepatomegaly, and coagulation abnormalities. An accumulation of Man1GlcNAc2-PP-dolichol and Man2GlcNAc2-PP-dolichol was observed in skin fibroblasts of the patient. Incubation of patient fibroblast extracts with Man1GlcNAc2-PP-dolichol and GDP-mannose revealed a severely reduced activity of the mannosyltransferase elongating Man1GlcNAc2-PP dolichol. Because the Saccharomyces cerevisiae mutant alg2-1 was known to accumulate the same shortened dolichol-linked oligosaccharides as the patient, the yeast ALG2 sequence was used to identify the human ortholog. Genetic analysis revealed that the patient was heterozygous for a single nucleotide deletion and a single nucleotide substitution in the human ortholog of yeast ALG2. Expression of wild type but not of mutant hALG2 cDNA restored the mannosyltransferase activity and the biosynthesis of dolichol-linked oligosaccharides both in patient fibroblasts and in the alg2-1 yeast cells. hALG2 was shown to act as an alpha1,3-mannosyltransferase. The resulting Manalpha1,3-ManGlcNAc2-PP dolichol is further elongated by a yet unknown alpha1,6-mannosyltransferase.
Thiel
Christian
C
Georg-August-Universität Göttingen, Biochemie II, Heinrich-Düker-Weg 12, D-37073 Göttingen, Germany.
Schwarz
Markus
M
Peng
Jianhe
J
Grzmil
Michal
M
Hasilik
Martin
M
Braulke
Thomas
T
Kohlschütter
Alfried
A
von Figura
Kurt
K
Lehle
Ludwig
L
Körner
Christian
C
D001483:Base Sequence; D002239:Carbohydrate Metabolism, Inborn Errors / Q000235:genetics*; D002240:Carbohydrate Sequence; D002460:Cell Line; D017931:DNA Primers; D004288:Dolichol Phosphates / Q000378:metabolism; D004286:Dolichols / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts; D005816:Genetic Complementation Test; D006031:Glycosylation; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009844:Oligosaccharides / Q000096:biosynthesis*; D010375:Pedigree; D011103:Polyisoprenyl Phosphate Monosaccharides / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D017931:DNA Primers; D004288:Dolichol Phosphates; D004286:Dolichols; D009844:Oligosaccharides; D011103:Polyisoprenyl Phosphate Monosaccharides; C026406:dolichol pyrophosphate; C018439:N-acetylglucosaminylpyrophosphoryldolichol