An FM3A mutant, G258, with a mutation that affects both cell growth and oligosaccharide-lipid synthesis

Cloning and transcriptional expression of mouse mannosyltransferase IV/V cDNA, which is involved in the synthesis of lipid-linked oligosaccharides

We cloned the mouse mannosyltransferase IV/V gene (mALG11) from FM3A cells by a bioinformatic approach. The ORF contained 1476 bp encoding 492 amino acids. The cloned mALG11 complemented the growth defect of the Saccharomyces cerevisiae ALG11Δ mutant. In addition, we detected a variant cDNA by alternate splicing that had an additional four-nucleotide ATGC insertion at base 276 of the ORF. Consequently the variant cDNA encoded a truncated protein with 92 amino acids, lacking the glycosyltransferase group-1 domain. The variant cDNA occurs in many mouse strains according to EST database searches. Moreover, we detected it in FM3A cDNA, but we did not detect any such variants in the human EST database or in HeLa cDNA, although human ALG11 (hALG11) genomic DNA has the same sequence around the intron-exon boundaries as those of mALG11 genomic DNA. Hence, we concluded that there is different transcriptional control mechanism between mALG11 and hALG11.

Remarkable expression in the colon adenocarcinoma of Hmat-Xa, a human mannosyltransferase-like gene, that is homologous to drosophila gene GC15914

We cloned a novel human mannosyltransferase-like gene, designated Hmat-Xa, as a gene homologous to the Drosophila GC15914 gene encoding the 9QVXN0 protein: see "Project Report for FY2002 on the 'Construction of Libraries of Human Genes Participating in Glycosylation' project" 43-45 (2003), New Energy and Industrial Technology Development Organization (NEDO), NEDO and Research Association for Biotechnology, Tokyo, Japan (in Japanese). After that, the GTDC1 gene, as reported by Zhao et al., DNA Cell Biol., 23, 183-187 (2004), was found to be the same as the Hmat-Xa gene. Domain EXFGI/L/VX(2)L/VE in the Hmat-Xa protein, also present in both human mannosyltransferase II/III and mannosyltransferase IV/V, which are involved in the synthesis of lipid-linked oligosaccharides, and some bacterial mannosyltransferases. A real-time PCR study of Hmat-Xa mRNA expression in human normal and tumor multiple tissue cDNA identified its tissue-specific expression and its remarkable expression in colon adenocarcinoma as compared to the normal counterpart. Thus the elevated expression of Hmat-Xa might serve as a candidate marker for colon adenocarcinoma.

Characterization of an alg2 mutant of the zygomycete fungus Rhizomucor pusillus

The zygomycete fungus Rhizomucor pusillus secretes an aspartic proteinase (MPP) that contains asparagine ( N )-linked oligosaccharides at two sites. Mutant strain 1116 defective in N -glycosylation secretes MPP with truncated oligo-saccharide chains. Lipid-linked oligosaccharides in mutant 1116 were labeled with [6-(3)H]glucosamine and [2-(3)H]mannose, prepared by cycles of solvent extraction, and analyzed by gel filtration chromatography on a Bio-Gel P-4 column after mild acid-hydrolysis. Mutant 1116 accumulated an intermediate, Man(1)GlcNAc(2)-dolichol pyrophosphate (PP-Dol), whereas wild-type strain F27 synthesized the fully assembled oligosaccharide precursor Glc(3)Man(9)GlcNAc(2)-PP-Dol. Consistent with this, alg2 encoding a mannosyltransferase in the lipid-linked oligosaccharide biosynthetic pathway in mutant 1116 had a 5 bp insertion that generated a stop codon in the middle of the coding sequence. Transformation of mutant 1116 with the intact alg2 gene on a pUC19-derived plasmid generated transformants that contained multicopies of alg2 at the alg2 locus. Glycosylation of the total proteins in the transformants was recovered to the same level as in strain F27, as determined with peroxidase-concanavalin A. These transformants produced MPP mainly with the same N -linked oligosaccharides as that produced by strain F27, but still with truncated oligosaccharides in small amounts. All of these data show that Alg2 is an alpha-1,3 or alpha-1,6 mannosyltransferase that elongates Man(1)GlcNAc(2)-PP-Dol to Man(2)GlcNAc(2)-PP-Dol. The slower growth of mutant 1116 was significantly recovered on introduction of alg2. The viability of the alg2 mutants of the zygomycete R.pusillus makes a contrast with the lethal effect of ALG2 mutations in the yeast Saccharomyces cerevisiae.