Self-regulation of MGAT4A and MGAT4B activity toward glycoproteins through interaction of lectin domain with their own N-glycans

Naoko Osada; Sushil K Mishra; Miyako Nakano; Yuko Tokoro; Masamichi Nagae; Robert J Doerksen; Yasuhiko Kizuka

doi:10.1016/j.isci.2024.111066

Self-regulation of MGAT4A and MGAT4B activity toward glycoproteins through interaction of lectin domain with their own N-glycans

iScience. 2024 Sep 28;27(11):111066. doi: 10.1016/j.isci.2024.111066. eCollection 2024 Nov 15.

Authors

Naoko Osada¹, Sushil K Mishra², Miyako Nakano³, Yuko Tokoro⁴, Masamichi Nagae^{5

6}, Robert J Doerksen², Yasuhiko Kizuka^{1

4}

Affiliations

¹ Graduate School of Natural Science and Technology, Gifu University, Gifu 501-1193, Japan.
² Glycoscience Center of Research Excellence, Department of BioMolecular Sciences, University of Mississippi, Oxford, MS 38677, USA.
³ Graduate School of Integrated Sciences for Life, Hiroshima University, Higashihiroshima 739-8530, Japan.
⁴ Institute for Glyco-core Research (iGCORE), Gifu University, Gifu 501-1193, Japan.
⁵ Department of Molecular Immunology, Research Institute for Microbial Diseases, Osaka University, Suita 565-0871, Japan.
⁶ Laboratory of Molecular Immunology, Immunology Frontier Research Center (IFReC), Osaka University, Suita 565-0871, Japan.

Abstract

N-Acetylglucosaminyltransferases-IVa (GnT-IVa or MGAT4A) and -IVb (MGAT4B) are glycosyltransferase isozymes synthesizing the β1,4-GlcNAc branch in N-glycans, a glycan structure involved in diabetes. These enzymes uniquely have a non-catalytic lectin domain, which selectively recognizes the GnT-IV product N-glycan branch, but the role of this lectin domain has remained unclear. Here, using UDP-Glo enzyme assays, we discovered that this domain is required for activity toward glycoprotein substrates but not toward free glycans. Furthermore, we found that the lectin domain itself is decorated with an N-glycan, which can serve as a self-ligand and interact with the ligand binding site of the lectin domain in a glycan structure-dependent manner. Enzyme assays using glycan-remodeled GnT-IVa demonstrated that the interaction of the self-ligand with the lectin domain suppresses GnT-IVa activity toward glycoprotein substrates. These findings unveiled a lectin-assisted self-regulatory mechanism of glycosyltransferases, which deepens our understanding of the complex pathway of N-glycan biosynthesis.

Keywords: Biochemistry; Biological sciences; Glycobiology; Molecular dynamics; Structural biology.