N-glycosylation and glycoprotein's fate in the fission yeast secretory pathway

ORSI, R.; OLSON, LJ; PETERSON, F.C; KIM, JP; PARODI, AJ; DAHMS, NM; D'ALESSIO, C

Guanajuato

Congreso; 3rd Latin American Congress of Glycobiology; 2015

Sociedad Latinoamericana de Glicobiología

N-glycosylationconsists of the transfer of a pre-assembled glycan (Glc3Man9GlcNAc2)from a lipid donor to consensus sequences within proteins that are entering theendoplasmic reticulum (ER). The protein-linked glycans are then processed inthe ER producing specific structures that serve as signalling molecules for thefate of the folding glycoprotein: to stay in the ER during the folding process,to be retrotranslocated to the cytosol for proteasomal degradation ifirreversibly misfolded, or to continue through the secretory pathway. GlucosidaseII (GII) is a key player of the quality control of glycoprotein folding mechanismin the ER. It sequentially removes the two innermost glucoses from the glycantransferred upon N-glycosylationand also a glucose residue added to folding intermediates byUDP-Glc:glycoprotein glucosyltransferase, a glycoprotein conformational sensor.GII is an ER soluble heterodimer composed of catalytic GIIalpha and regulatory GII beta subunits. We showed that GIIbeta is involved in GIIalpha's ER localization and in N-glycan recognition through its C-terminal mannose 6-phosphate receptor homology (MRH) domain. Also, we showedthat GII regulates the permanence of slow folding proteins in the ER as it displaysa decreased activity toward demannosylated N-glycans present in such species, thus prolonging thehalf-lives of monoglucosylated glycans able to interact with the ERlectin/chaperone calnexin. We determined the structure of a functional isolated GIIbeta MRH domain, which revealed the conserved fold observed in other MRH-containingproteins of the secretory pathway. Conserved residues in GIIbeta MRH domain wereidentified that provide insight to understand how GIIbeta influences GII glucosetrimming