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

GALLO GIOVANNA LUCRECIA; VALKO, AYELEN; IDROVO, TOMMY; ETCHEGARAY, EMILIANA; ARAMBURU, SOFÍA IVANA; D'ALESSIO CECILIA

Boston

Conferencia; First International Conference on Cell and Experimental Biology CEB-2020; 2020

Cell and Experimental Biology CEB

Congenital Disorders of Glycosylation (CDGs) are a group of human inherited multi-systemic diseases. Many are due to defects in protein N- glycosylation, in which an evolutionary conserved pre-assembled glycan Glc3Man9ClcNAc2 (G3M9) is transferred by the oligosaccharyltransferase (OST) from a donor lipid to proteins that are entering into the endoplasmic reticulum (ER). Defects in glycan remodeling afterwards produce CDG Type II. Glucosidase I (GI) is the first glycan-remodeling enzyme that removes the outermost glucose, and mutations in GI-encoding gene (gls1+) result in CDG-IIb. Using the fission yeast Schizosaccharomyces pombe lacking GI as a model organism we demonstrated that the main cause of the morphological and growth defects observed in mutant cells was the persistence of G3M9 structures in glycoproteins, as a second mutation in alg10+ gene (responsible for the addition of the last Glc during the lipid-linked G3M9 synthesis) substantially suppressed the observed defects. The sick phenotype 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 to a potentially reduced ER-associated degradation. Further analysis showed that the endomembrane system was altered in cells lacking GI, as cell wall glycoproteins region was wider in Δgls1 cells than in WT ones and as the lack of GI produces cells with highly fragmented vacuoles. Collectively, these results suggest the occurrence of alterations in the secretory/endocytic pathway in cells lacking GI and shed light on the underlying molecular and cellular mechanisms of CDG IIb disease.