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J Biol Chem. 2018 May 4;293(18):6707-6720. doi: 10.1074/jbc.RA117.000782. Epub 2018 Feb 23.

Identification of multiple isomeric core chitobiose-modified high-mannose and paucimannose N-glycans in the planarian Schmidtea mediterranea.

Author information

1
From the Institute for Stem Cell Biology and Regenerative Medicine (inStem), GKVK Post Office, Bellary Road, Bangalore 560065, Karnataka, India and.
2
Glycomics and Glycoproteomics Facility, Centre for Cellular and Molecular Platforms (C-CAMP), GKVK Post Office, Bellary Road, Bangalore 560065, Karnataka, India ponbabu@gmail.com.
3
From the Institute for Stem Cell Biology and Regenerative Medicine (inStem), GKVK Post Office, Bellary Road, Bangalore 560065, Karnataka, India and ramas@instem.res.in.

Abstract

Cell surface-associated glycans mediate many cellular processes, including adhesion, migration, signaling, and extracellular matrix organization. The galactosylation of core fucose (GalFuc epitope) in paucimannose and complex-type N-glycans is characteristic of protostome organisms, including flatworms (planarians). Although uninvestigated, the structures of these glycans may play a role in planarian regeneration. Whole-organism MALDI-MS analysis of N-linked oligosaccharides from the planarian Schmidtea mediterranea revealed the presence of multiple isomeric high-mannose and paucimannose structures with unusual mono-, di-, and polygalactosylated (n = 3-5) core fucose structures; the latter structures have not been reported in other systems. Di- and trigalactosylated core fucoses were the most dominant glycomers. N-Glycans showed extensive, yet selective, methylation patterns, ranging from non-methylated to polymethylated glycoforms. Although the majority of glycoforms were polymethylated, a small fraction also consisted of non-methylated glycans. Remarkably, monogalactosylated core fucose remained unmethylated, whereas its polygalactosylated forms were methylated, indicating structurally selective methylation. Using database searches, we identified two potential homologs of the Galβ1-4Fuc-synthesizing enzyme from nematodes (GALT-1) that were expressed in the prepharyngeal, pharyngeal, and mesenchymal regions in S. mediterranea. The presence of two GALT-1 homologs suggests different requirements for mono- and polygalactosylation of core fucose for the formation of multiple isomers. Furthermore, we observed variations in core fucose glycosylation patterns in different planarian strains, suggesting evolutionary adaptation in fucose glycosylation. The various core chitobiose modifications and methylations create >60 different glycoforms in S. mediterranea. These results contribute greatly to our understanding of N-glycan biosynthesis and suggest the presence of a GlcNAc-independent biosynthetic pathway in S. mediterranea.

KEYWORDS:

GALT-1; Galβ1–4Fuc; N-linked glycosylation; O-methylation; S. mediterranea; antisense RNA; galactosyltransferase; invertebrate; mass spectrometry (MS); planaria

PMID:
29475940
PMCID:
PMC5936828
DOI:
10.1074/jbc.RA117.000782
[Indexed for MEDLINE]
Free PMC Article

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