Glucosidase II beta subunit modulates N-glycan trimming in fission yeasts and mammals.
Glucosidase II (GII) plays a key role in glycoprotein biogenesis in the endoplasmic reticulum (ER). It is responsible for the sequential removal of the two innermost glucose residues from the glycan (Glc(3)Man(9)GlcNAc(2)) transferred to Asn residues in proteins. GII participates in the calnexin/calreticulin cycle; it removes the single glucose unit added to folding intermediates and misfolded glycoproteins by the UDP-Glc:glycoprotein glucosyltransferase. GII is a heterodimer whose alpha subunit (GIIalpha) bears the glycosyl hydrolase active site, whereas its beta subunit (GIIbeta) role is controversial and has been reported to be involved in GIIalpha ER retention and folding. Here, we report that in the absence of GIIbeta, the catalytic subunit GIIalpha of the fission yeast Schizosaccharomyces pombe (an organism displaying a glycoprotein folding quality control mechanism similar to that occurring in mammalian cells) folds to an active conformation able to hydrolyze p-nitrophenyl alpha-d-glucopyranoside. However, the heterodimer is required to efficiently deglucosylate the physiological substrates Glc(2)Man(9)GlcNAc(2) (G2M9) and Glc(1)Man(9)GlcNAc(2) (G1M9). The interaction of the mannose 6-phosphate receptor homologous domain present in GIIbeta and mannoses in the B and/or C arms of the glycans mediates glycan hydrolysis enhancement. We present evidence that also in mammalian cells GIIbeta modulates G2M9 and G1M9 trimming.
Stigliano
Ivan D
ID
Laboratories of Glycobiology and Structural Cell Biology, Fundación Instituto Leloir, Consejo Nacional de Investigaciones Científicas y Técnicas, C1405BWE, Buenos Aires, Argentina.
Caramelo
Julio J
JJ
Labriola
Carlos A
CA
Parodi
Armando J
AJ
D'Alessio
Cecilia
C
D000595:Amino Acid Sequence; D000818:Animals; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D020134:Catalytic Domain; D005960:Glucosides / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011134:Polysaccharides / Q000378:metabolism*; D017510:Protein Folding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017527:Receptor, IGF Type 2 / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000201:enzymology; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D000520:alpha-Glucosidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D005960:Glucosides; D007527:Isoenzymes; D011134:Polysaccharides; D021122:Protein Subunits; D017527:Receptor, IGF Type 2; D029702:Schizosaccharomyces pombe Proteins; C019502:4-nitrophenyl alpha-glucoside; C034251:4-nitrophenyl-alpha-glucosidase; D000520:alpha-Glucosidases