The 48-kDa subunit of the mammalian oligosaccharyltransferase complex is homologous to the essential yeast protein WBP1

UMMS Affiliation

Department of Biochemistry and Molecular Biology

Publication Date


Document Type



Amino Acid Sequence; Animals; Base Sequence; Cell Line; Cloning, Molecular; Dogs; Fungal Proteins; *Hexosyltransferases; Macromolecular Substances; Membrane Proteins; Microsomes; Molecular Sequence Data; Molecular Weight; Pancreas; Polymerase Chain Reaction; Restriction Mapping; Saccharomyces cerevisiae; Sequence Homology, Amino Acid; Transferases


Life Sciences | Medicine and Health Sciences


Oligosaccharyltransferase has been purified from canine microsomal membranes as a protein complex with three nonidentical subunits of 66, 63/64, and 48 kDa. The 66- and 63/64-kDa subunits were found to be identical to ribophorins I and II, respectively. The ribophorins are integral membrane glycoproteins that were previously shown to be localized exclusively to the rough endoplasmic reticulum. The 48-kDa subunit (OST48) of the oligosaccharyltransferase complex is not a glycoprotein and is not recognized by antibodies to either ribophorin. Here, we describe the characterization of a cDNA clone that encodes OST48. Like ribophorins I and II, OST48 was found to be an integral membrane protein, with the majority of the polypeptide located within the lumen of the endoplasmic reticulum. OST48 does not show significant amino acid sequence homology to either ribophorin I or II. A 45-kDa integral membrane protein, designated WBP1, from the yeast Saccharomyces cerevisiae was found to be 25% identical in sequence to OST48. Recently, WBP1 was shown to be essential for in vivo and in vitro expression of oligosaccharyltransferase activity in yeast. We conclude that OST48 and WBP1 are homologous gene products.


J Biol Chem. 1992 Nov 25;267(33):23658-63.

Journal/Book/Conference Title

The Journal of biological chemistry glycotransferase)

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