title: Endoplasmic reticulum glucosidase II is inhibited by its end products.
abstract: The calnexin/calreticulin cycle is a quality control system responsible for promoting the folding of newly synthesized glycoproteins entering the endoplasmic reticulum (ER). The association of calnexin and calreticulin with the glycoproteins is regulated by ER glucosidase II, which hydrolyzes Glc 2Man X GlcNAc 2 glycans to Glc 1Man X GlcNAc 2 and further to Glc 0Man X GlcNAc 2 ( X represents any number between 5 and 9). To gain new insights into the reaction mechanism of glucosidase II, we developed a kinetic model that describes the interactions between glucosidase II, calnexin/calreticulin, and the glycans. Our model accurately reconstructed the hydrolysis of glycans with nine mannose residues and glycans with seven mannose residues, as measured by Totani et al. [Totani, K., Ihara, Y., Matsuo, I., and Ito, Y. (2006) J. Biol. Chem. 281, 31502-31508]. Intriguingly, our model predicted that glucosidase II was inhibited by its nonglucosylated end products, where the inhibitory effect of Glc 0Man 7GlcNAc 2 was much stronger than that of Glc 0Man 9GlcNAc 2. These predictions were confirmed experimentally. Moreover, our model suggested that glycans with a different number of mannose residues can be equivalent substrates of glucosidase II, in contrast to what had been previously thought. We discuss the possibility that nonglucosylated glycans, existing in the ER, might regulate the entry of newly synthesized glycoproteins into the calnexin/calreticulin cycle. Our model also shows that glucosidase II does not interact with monoglucosylated glycans while they are bound to calnexin or calreticulin.
authors.affiliation: Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Eran
authors.initials: E
authors.lastname: Bosis
authors.forename: Esther
authors.initials: E
authors.lastname: Nachliel
authors.forename: Tamar
authors.initials: T
authors.lastname: Cohen
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Takeda
authors.forename: Yukishige
authors.initials: Y
authors.lastname: Ito
authors.forename: Shoshana
authors.initials: S
authors.lastname: Bar-Nun
authors.forename: Menachem
authors.initials: M
authors.lastname: Gutman
mesh_terms: D000465:Algorithms; D002851:Chromatography, High Pressure Liquid; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D065089:Glycoside Hydrolase Inhibitors; D006031:Glycosylation; D006868:Hydrolysis; D007700:Kinetics; D000520:alpha-Glucosidases
chemical_list: D065089:Glycoside Hydrolase Inhibitors; C034251:4-nitrophenyl-alpha-glucosidase; D000520:alpha-Glucosidases