Oxidoreductase activity of oligosaccharyltransferase subunits Ost3p and Ost6p defines site-specific glycosylation efficiency.
Asparagine-linked glycosylation is a common posttranslational modification of diverse secretory and membrane proteins in eukaryotes, where it is catalyzed by the multiprotein complex oligosaccharyltransferase. The functions of the protein subunits of oligoasccharyltransferase, apart from the catalytic Stt3p, are ill defined. Here we describe functional and structural investigations of the Ost3/6p components of the yeast enzyme. Genetic, biochemical and structural analyses of the lumenal domain of Ost6p revealed oxidoreductase activity mediated by a thioredoxin-like fold with a distinctive active-site loop that changed conformation with redox state. We found that mutation of the active-site cysteine residues of Ost6p and its paralogue Ost3p affected the glycosylation efficiency of a subset of glycosylation sites. Our results show that eukaryotic oligosaccharyltransferase is a multifunctional enzyme that acts at the crossroads of protein modification and protein folding.
Schulz
Benjamin L
BL
Institute of Microbiology, Department of Biology, Eidgenössische Technische Hochschule Zurich, 8093 Zurich, Switzerland.
Stirnimann
Christian U
CU
Grimshaw
John P A
JP
Brozzo
Maurice S
MS
Fritsch
Fabienne
F
Mohorko
Elisabeth
E
Capitani
Guido
G
Glockshuber
Rudi
R
Grütter
Markus G
MG
Aebi
Markus
M
D020816:Amino Acid Motifs; D020134:Catalytic Domain; D006031:Glycosylation; D006602:Hexosyltransferases / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D010088:Oxidoreductases / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000378:metabolism
D008565:Membrane Proteins; D010455:Peptides; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; D013438:Sulfhydryl Compounds; D010088:Oxidoreductases; D006602:Hexosyltransferases; C507060:OST6 protein, S cerevisiae; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase