Based on limited published evidence, POFUT4 is a protein O-fucosyltransferase that catalyzes O-fucosylation of serine or threonine residues in elastin microfibril interface (EMI) domains of target proteins including MMRN1, MMRN2, and EMID1 1. The enzyme attaches fucose through O-glycosidic linkages and localizes to the endoplasmic reticulum, where O-fucosylation of EMI domain-containing proteins facilitates protein folding and secretion 1. POFUT4 also demonstrates minor alpha-(1,3)-fucosyltransferase activity toward biantennary N-glycan acceptors in synthetic substrate libraries, though in vivo relevance remains unclear 2.