MGAT4B is a Golgi-localized glycosyltransferase that catalyzes the transfer of N-acetylglucosamine (GlcNAc) to complex-type N-linked glycans, preferentially generating tri- and tetra-antennary sugar chain structures 1. The enzyme transfers GlcNAc from UDP-GlcNAc to the α1-3 arm of N-glycan cores through β1-4 linkage 2. MGAT4B exhibits lower substrate affinity than its isozyme MGAT4A, suggesting a secondary role in normal N-glycan biosynthesis 1. Functionally, MGAT4B regulates N-glycosylation of key melanocyte proteins including GPNMB, KIT, and TYRP1, controlling directional cell migration and melanocyte stem cell pool establishment 3. The enzyme localizes to Golgi membranes and forms functional complexes with nucleotide sugar transporters 4. Clinically, elevated MGAT4B expression in BRAFV600E-mutant melanoma patients correlates with significantly worse survival outcomes 3. Mechanistically, MGAT4B-mediated complex N-glycosylation promotes cell-cell adhesion and tumor initiation, with small-molecule inhibitors of complex N-glycosylation showing promise in suppressing early-stage melanoma progression 3. Additionally, MGAT4B has been identified as a causal risk factor for coronary artery disease through proteome-integrated genetic analysis 5, and its expression is associated with aggressive prostate adenocarcinoma phenotypes 6.