The 3.4-kDa Ost4 protein is required for the assembly of two distinct oligosaccharyltransferase complexes in yeast.
In the central reaction of N-linked glycosylation, the oligosaccharyltransferase (OTase) complex catalyzes the transfer of a lipid-linked core oligosaccharide onto asparagine residues of nascent polypeptide chains in the lumen of the endoplasmic reticulum (ER). The Saccharomyces cerevisiae OTase has been shown to consist of at least eight subunits. We analyzed this enzyme complex, applying the technique of blue native gel electrophoresis. Using available antibodies, six different subunits were detected in the wild-type (wt) complex, including Stt3p, Ost1p, Wbp1p, Swp1p, Ost3p, and Ost6p. We demonstrate that the small 3.4-kDa subunit Ost4p is required for the incorporation of either Ost3p or Ost6p into the complex, resulting in two, functionally distinct OTase complexes in vivo. Ost3p and Ost6p are not absolutely required for OTase activity, but modulate the affinity of the enzyme toward different protein substrates.
Spirig
Urs
U
Institute of Microbiology, ETH Zurich, CH-8093 Zurich, Switzerland.
Bodmer
Daniel
D
Wacker
Michael
M
Burda
Patricie
P
Aebi
Markus
M
D002384:Catalysis; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry; D017353:Gene Deletion; D006031:Glycosylation; D006602:Hexosyltransferases / Q000737:chemistry* / Q000502:physiology*; D007700:Kinetics; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry* / Q000502:physiology*; D009844:Oligosaccharides / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology; D013696:Temperature; D013997:Time Factors
D005656:Fungal Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009844:Oligosaccharides; D010455:Peptides; D029701:Saccharomyces cerevisiae Proteins; D006602:Hexosyltransferases; C507060:OST6 protein, S cerevisiae; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase