Oxidoreductase activity of oligosaccharyltransferase subunits Ost3p and Ost6p defines site-specific glycosylation efficiency.

Benjamin L Schulz, Christian U Stirnimann, John P A Grimshaw, Maurice S Brozzo, Fabienne Fritsch, Elisabeth Mohorko, Guido Capitani, Rudi Glockshuber, Markus G Grütter, Markus Aebi

Institute of Microbiology, Department of Biology, Eidgenössische Technische Hochschule Zurich, 8093 Zurich, Switzerland.

Proceedings of the National Academy of Sciences of the United States of America 2009 Jul 7

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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.

Citation

Benjamin L Schulz, Christian U Stirnimann, John P A Grimshaw, Maurice S Brozzo, Fabienne Fritsch, Elisabeth Mohorko, Guido Capitani, Rudi Glockshuber, Markus G Grütter, Markus Aebi. Oxidoreductase activity of oligosaccharyltransferase subunits Ost3p and Ost6p defines site-specific glycosylation efficiency. Proceedings of the National Academy of Sciences of the United States of America. 2009 Jul 7;106(27):11061-6