GLUCOSIDASE II: FROM GLYCOPROTEIN FOLDING QUALITY CONTROL TO THE STRUCTURE OF ITS LECTIN MRH DOMAIN

ORSI, R; OLSON, L. J.; DAHMS, N. M.; D'ALESSIO, C.

Simposio; 1er Simposio Argentino de Glicobiología - GLYCOAR 2014; 2014

Glucosidase II (GII) is a key player of the quality control of glycoprotein folding in the endoplasmic reticulum (ER) that ensures that only properly folded glycoproteins reach their final destination in the cell. GII sequentially removes the two innermost glucoses from the Glc3Man9GlcNAc2 glycan transferred upon protein N-glycosylation and also the glucose residue added to folding intermediates by UDP-Glc:glycoprotein glucosyltransferase, a glycoprotein conformational sensor. GII is an ER luminal heterodimer composed of a catalytic GIIα and regulatory GIIβ subunits. Our work showed that GIIβ is involved in GIIα?s ER localization and N-glycan recognition through its C-terminal mannose 6-phosphate receptor homology (MRH) domain. Also, we showed that GII regulates the permanence of slow folding proteins in the ER as it displays a decreased activity toward demannosylated N-glycans present in such species, thus prolonging the half-lives of monoglucosylated glycans able to interact with ER lectin/chaperones calreticulin and calnexin. We determined the structure of a functional isolated GIIβ MRH domain, which revealed the conserved fold observed in other MRH-containing proteins of the secretory pathway as the mannose 6-phosphate receptors and OS-9. Conserved residues in GIIβ MRH domain were identified that provide insight into how GIIβ influences GII glucose trimming activity in vivo.