2. Academic Validation
  3. Examination of differential glycoprotein preferences of N-acetylglucosaminyltransferase-IV isozymes a and b

Examination of differential glycoprotein preferences of N-acetylglucosaminyltransferase-IV isozymes a and b

  • J Biol Chem. 2022 Sep;298(9):102400. doi: 10.1016/j.jbc.2022.102400.
Naoko Osada 1,  Masamichi Nagae 2,  Miyako Nakano 3,  Tetsuya Hirata 4,  Yasuhiko Kizuka 5
Affiliations

Affiliations

  • 1 Faculty of Applied Biological Sciences, Gifu University, Gifu, Japan.
  • 2 Department of Molecular Immunology, Research Institute for Microbial Diseases, Osaka University, Suita, Japan; Laboratory of Molecular Immunology, Immunology Frontier Research Center (iFReC), Osaka University, Suita, Japan.
  • 3 Graduate School of Integrated Sciences for Life, Hiroshima University, Higashihiroshima, Japan.
  • 4 Institute for Glyco-Core Research (iGCORE), Gifu University, Gifu, Japan.
  • 5 Faculty of Applied Biological Sciences, Gifu University, Gifu, Japan; Institute for Glyco-Core Research (iGCORE), Gifu University, Gifu, Japan. Electronic address: kizuka@gifu-u.ac.jp.
PMID: 35988645 DOI: 10.1016/j.jbc.2022.102400
Abstract

The N-glycans attached to proteins contain various GlcNAc branches, the aberrant formation of which correlates with various diseases. N-Acetylglucosaminyltransferase-IVa (GnT-IVa or MGAT4A) and Gnt-IVb (or MGAT4B) are isoenzymes that catalyze the formation of the β1,4-GlcNAc branch in N-glycans. However, the functional differences between these isozymes remain unresolved. Here, using cellular and UDP-Glo Enzyme assays, we discovered that GnT-IVa and GnT-IVb have distinct glycoprotein preferences both in cells and in vitro. Notably, we show that GnT-IVb acted efficiently on glycoproteins bearing an N-glycan premodified by GnT-IV. To further understand the mechanism of this reaction, we focused on the noncatalytic C-terminal lectin domain, which selectively recognizes the product glycans. Replacement of a nonconserved amino acid in the GnT-IVb lectin domain with the corresponding residue in GnT-IVa altered the glycoprotein preference of GnT-IVb to resemble that of GnT-IVa. Our findings demonstrate that the C-terminal lectin domain regulates differential substrate selectivity of GnT-IVa and GnT-IVb, highlighting a new mechanism by which N-glycan branches are formed on glycoproteins.

Keywords

GnT-IV; glycobiology; glycoprotein biosynthesis; glycosylation; glycosyltransferase; substrate specificity.

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