Molecular dissection of Glucosidase II, a key element in preventing glycoprotein misfolding” Stigliano, I.; Labriola, C.; Caramelo, J.; D’Alessio, C and Parodi, A. . May 13-15 2009,

STIGLIANO, I.D.; CARAMELO, J; LABRIOLA, C.A.; D'ALESSIO, C.; PARODI, A.J.

Tel Aviv University, Israel

Conferencia; Protein misfolding in the test tube and disease; 2009

Tel Aviv University

Glucosidase II (GII) is a key player in glycoprotein biogenesis in the endoplasmic reticulum (ER) as it is responsible for the sequential removal of the two innermost glucose residues from the glycan (Glc3Man9GlcNac2) transferred to Asn residues in proteins (N-glycosylation). Furthermore, GII participates in the so called calnexin/calreticulin cycle as it removes the single glucose unit added to folding intermediates and misfolded glycoproteins by the UDP-Glc:glycoprotein glucosyltransferase. GII is a heterodimer whose alfa subunit (GIIa) bears the glycosyl hydrolase active site. The beta subunit (GIIb) has been reported to be involved in GIIa ER retention, maturation, glycan recognition as well as in cell development and human disease. Here we report that in the absence of GIIb the catalytic subunit (GIIa) of the fission yeast Schizosaccharomyces pombe (an organism displaying a glycoprotein folding quality control mechanism similar to that ocurring in mammalian cells) matures to an active conformation able to hydrolyze the substrate analogue p-nitrophenyl glucoside (pNPG) but very poorly the psyshiological substrates Glc2Man9GlcNac (G2M9) and Glc1Man9GlcNac (G1M9) and is sub optimally retained in the ER. However the GIIa/GIIb heterodimer is required to efficiently deglucosylate both G2M9 and G1M9. The interaction of the mannose 6-phosphate receptor domain present in GIIb and mannoses in the B and/or C arms of the glycans mediates glycan hydrolysis enhancement. In addition, the VDEL sequence present at the GIIb C-terminus is required for optimal ER GII localization. Evidence is presented that also in mammalian cells GIIb modulates G2M9 and G1M9 deglucosylation.