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Graphical Abstract
Highlights
Loss of bisecting GlcNAc in N-glycan increases various terminal glycan modifications.
Glycosyltransferases commonly do not act well on glycans with bisecting GlcNAc.
Presence of bisecting GlcNAc alters overall conformation of N-glycan.
Bisecting GlcNAc serves as a general suppressor for terminal modification.
Abstract
Glycoproteins are decorated with complex glycans for protein functions. However, regulation mechanisms of complex glycan biosynthesis are largely unclear. Here we found that bisecting GlcNAc, a branching sugar residue in N-glycan, suppresses the biosynthesis of various types of terminal epitopes in N-glycans, including fucose, sialic acid and human natural killer-1. Expression of these epitopes in N-glycan was elevated in mice lacking the biosynthetic enzyme of bisecting GlcNAc, GnT-III, and was conversely suppressed by GnT-III overexpression in cells. Many glycosyltransferases for N-glycan terminals were revealed to prefer a nonbisected N-glycan as a substrate to its bisected counterpart, whereas no up-regulation of their mRNAs was found. This indicates that the elevated expression of the terminal N-glycan epitopes in GnT-III-deficient mice is attributed to the substrate specificity of the biosynthetic enzymes. Molecular dynamics simulations further confirmed that nonbisected glycans were preferentially accepted by those glycosyltransferases. These findings unveil a new regulation mechanism of protein N-glycosylation.
- Glycomics
- glycoprotein pathways
- glycosylation
- glycoproteins
- glycoprotein structure
- glycoproteomics
- bisecting GlcNAc
- fucosylation
- GnT-III
- HNK-1
- sialylation
Footnotes
Author contributions: M.N., S.K.M., Y.T., K.S., K.N., and Y.K. performed research; M.N., K.N., Y.Y., N.T., and Y.K. analyzed data; S.K.M., Y.Y., and Y.K. wrote the paper; Y.K. designed research; Y.K. contributed new reagents/analytic tools.
↵* This work was supported by Grant-in-Aid for Scientific Research (C) to Y.K. [17K07356], Leading Initiative for Excellent Young Researchers (LEADER) project to Y.K. from the Japan Society for the Promotion of Science (JSPS), by Takeda Science Foundation, and by Mochida Memorial Foundation for Medical and Pharmaceutical Research.
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This article contains supplemental Figures and Tables.
- Received April 29, 2019.
- Revision received August 1, 2019.
- © 2019 Nakano et al.
Published under exclusive license by The American Society for Biochemistry and Molecular Biology, Inc.