Persistence of three but not two Glc in glycoproteins produces severe defects in fission yeasts

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

Partido de San Martín, Buenos Aires

Simposio; 3rd Argentinean Glycobiology Symposium "GlycoAr 2019"; 2019

Universidad Nacional de San Martín

Glucosidase I (GI) is an endoplasmic reticulum (ER) membraneprotein that removes the outermost Glc from Glc3Man9GlcNAc2(G3M9) transferred to proteins. Deficiency of GI results in congenitaldisorder of glycosylation (CDG) IIb. In fission yeasts, lack of GI (Δgls1-S mutants) resulted in a very sick phenotype and accumulation ofG3M9 protein-linked glycans. Surprisingly, mutants lackingglucosidase II, which display protein-linked G2M9, have a normalgrowth phenotype. This suggests that persistence of three but not twoGlc in glycoproteins is deleterious for the cell. While searching Δgls1mutants, we obtained a second strain with a healthier phenotype(Δgls1-H) that presented both G3M9 and Man9GlcNAc2 species. Thisstrain had an additional spontaneous mutation in gene alg10 (addsoutermost Glc during Dol-PP-G3M9 synthesis) thus producing NlinkedG2M9, and bypassing the need for GI. Moreover, expressionof Golgi human endomannosidase in Δgls1-S cells relieved the sickphenotype observed in this mutant, confirming that persistence ofG3M9 species in glycoproteins is deleterious. As the phenotypereversion was not a complete one in either case we expressed twocatalytic mutants of GI, resulting in a partial phenotype rescue.Altogether, these results would indicate that persistence of G3M9 inglycoproteins is at least in part responsible for the defects observed inthe CDG-IIb disorder and also suggest that GI might have anadditional function besides the catalytic one.