Fission yeast mutant lacking glucosidase I as a model for human congenital disorders of glycosylation CDG IIb

VALKO, A.; ETCHEGARAY, E.; GALLO, G.L.; PARODI, A.J.; ARAMBURU, S.I.; DALESSIO, C.

Buenos Aires

Simposio; 3rd Argentinian Symposium on Glycobiology; 2019

Glucosidase I (GI) plays a key role in the N-glycan remodeling in the secretory pathway, removing the outermost Glc from protein-linked Glc3Man9GlcNAc2 (G3M9). Mutations in GI-encoding gene results in human congenital disorders of glycosylation (CDG) IIb. Deletion of the homologous gene in Schizosaccharomyces pombe produced cells with a very sick phenotype (Δgls1) that could not be ascribed to the inability of glycoproteins to enter into calnexin-folding cycles, to an inhibition of the oligosaccharyltransferase transfer reaction or to a potentially reduced ERAD. Glycan elongation of glycoproteins in the Golgi and the overall cell wall (CW) monosaccharide composition of Δgls1 mutants were indistinguishable from that in cells lacking Glucosidase II (Δgls2α), whose phenotype is normal. However, transmission electron microscopy showed that the CW of Δgls1 was thicker than the WT and Δgls2α ones, presented a feathered appearance, and lacked the characteristic three-layered structure. Fluorescence-labeled lectin staining confirmed that the CW of Δgls1 cells had an altered structure. The ER localized below the plasma membrane was also absent in Δgls1 cells, indicating that the secretory pathway structure may be altered in this mutants, which constitute an excellent model organism for the study of CDG-IIb.