Galactosyltransferase 4 is a major control point for glycan branching in N-linked glycosylation

• Published in: Journal of cell science Vol. 127; no. Pt 23; pp. 5014 - 5026
• Main Authors: McDonald, Andrew G, Hayes, Jerrard M, Bezak, Tania, Głuchowska, Sonia A, Cosgrave, Eoin F J, Struwe, Weston B, Stroop, Corné J M, Kok, Han, van de Laar, Teun, Rudd, Pauline M, Tipton, Keith F, Davey, Gavin P
• Format: Journal Article
• Language: English
• Published: England The Company of Biologists 01-12-2014
• Subjects: Acetylglucosamine - metabolism; Animals; CHO Cells; Chorionic Gonadotropin - chemistry; Chorionic Gonadotropin - genetics; Chorionic Gonadotropin - metabolism; Chorionic Gonadotropin - pharmacology; Computer Simulation; Cricetulus; Glycosylation; HEK293 Cells; Humans; Isoenzymes; Kinetics; Male; Models, Biological; Models, Molecular; N-Acetylglucosaminyltransferases - chemistry; N-Acetylglucosaminyltransferases - genetics; N-Acetylglucosaminyltransferases - metabolism; Protein Conformation; Protein Processing, Post-Translational; Rats; Seminal Vesicles - drug effects; Seminal Vesicles - growth & development; Structure-Activity Relationship; Transfection; Galactosyltransferase; Glycosylation; Golgi; Chorionic gonadotropin; branching; hCG
• ISSN: 0021-9533; 1477-9137
• DOI: 10.1242/jcs.151878

Protein N-glycosylation is a common post-translational modification that produces a complex array of branched glycan structures. The levels of branching, or antennarity, give rise to differential biological activities for single glycoproteins. However, the precise mechanism controlling the glycan branching and glycosylation network is unknown. Here, we constructed quantitative mathematical models of N-linked glycosylation that predicted new control points for glycan branching. Galactosyltransferase, which acts on N-acetylglucosamine residues, was unexpectedly found to control metabolic flux through the glycosylation pathway and the level of final antennarity of nascent protein produced in the Golgi network. To further investigate the biological consequences of glycan branching in nascent proteins, we glycoengineered a series of mammalian cells overexpressing human chorionic gonadotropin (hCG). We identified a mechanism in which galactosyltransferase 4 isoform regulated N-glycan branching on the nascent protein, subsequently controlling biological activity in an in vivo model of hCG activity. We found that galactosyltransferase 4 is a major control point for glycan branching decisions taken in the Golgi of the cell, which might ultimately control the biological activity of nascent glycoprotein.