Unraveling the molecular bases of human congenital disorders of glycosylation using fission yeast as experimental model

GALLO, GIOVANNA L.; VALKO, AYELÉN; IDROVO, TOMMY; ETCHEGARAY, EMILIANA; ARAMBURU, SOFÍA I.; D'ALESSIO, C (CORRESPONDING AUTHOR)

Boston

Congreso; Cell and Experimental Biology (CEB 2020); 2020

naegaray, Sofía I. Aramburu, Cecilia DAlessio

CongenitalDisorders of Glycosylation (CDGs) are a group of human inherited multi-systemicdiseases. Many are due todefects in protein N- glycosylation,in which an evolutionary conserved pre-assembled glycan Glc3Man9ClcNAc2(G3M9) is transferred by the oligosaccharyltransferase (OST) from a donor lipidto proteins that are entering into the endoplasmic reticulum (ER). Defects inglycan remodeling afterwards produce CDG Type II. Glucosidase I (GI) is thefirst glycan-remodeling enzyme that removes the outermost glucose, and mutations inGI-encoding gene (gls1+)result in CDG-IIb. Using the fission yeast Schizosaccharomyces pombelacking GI as a model organism we demonstrated that the main cause of themorphological and growth defects observed in mutant cells was the persistenceof G3M9 structures in glycoproteins, as a second mutation in alg10+gene (responsible for the addition of the last Glc during the lipid-linked G3M9synthesis) substantially suppressed the observed defects. The sickphenotype of Δgls1 mutant cells could not be ascribed to a product inhibition of OST transfer reaction,to the inability of glycoproteins to enter into calnexin-folding cycles, or toa potentially reduced ER-associated degradation. Further analysis showed thatthe endomembranesystem was altered in cells lacking GI, as cell wallglycoproteins region was wider in Δgls1cells than in WT ones and as thelack of GI produces cells with highlyfragmented vacuoles. Collectively, these results suggest the occurrence ofalterations in the secretory/endocytic pathway in cells lacking GI and shedlight on the underlying molecular and cellular mechanisms of CDG IIb disease.