The cytoplasmic tail of alpha 1,2-fucosyltransferase contains a sequence for Golgi localization

The Golgi apparatus has a central role in the glycosylation of proteins and lipids. There is a sequential addition of carbohydrates by glycosyltransfe rases that are distributed within the Golgi in the order in which the glyco sylation occurs. The mechanism of glycosyltransferase retention is consider ed to involve their transmembrane domains and flanking regions, although we have shown that the cytoplasmic tail of alpha1,2-fucosyltransferase is imp ortant for its Golgi localization Here we show that the removal of the alph a1,2-fucosyltransferase cytoplasmic tail altered its function of fucosylati on and its localization site. When the tail was removed, the enzyme moved f rom the Gels to the trans Golgi network, suggesting that the transmembrane is responsible for retention and that the cytoplasmic tail is responsible f or localization. The cytoplasmic tail of alpha1,2-fucosyltransfefase contai ns 8 amino acids (MWVPSRRH), and mutating these to alanine indicated a role for amino acids 3 to 7 in localization with a particular role of Sers. Mut agenesis of Ser(5) to amino acids containing an hydroxyl (Tyr and Thr) demo nstrated that the hydroxyl at position 5 is important. Thus, the cytoplasmi c tail, and especially a single amino acid, has a predominant role in the l ocalization and thus the function of alpha1,2-fucosyltransferase.