Glycosylation site binding protein, a component of oligosaccharyl transferase, is highly similar to three other 57 kd luminal proteins of the ER.

A 57 kd component of oligosaccharyl transferase, termed glycosylation site binding protein, specifically recognizes a photoaffinity probe containing the N-glycosylation site sequence Asn-Lys-Thr. It is present in the lumen of the ER (endoplasmic reticulum) and its release from this compartment results in a loss of N-glycosylation. Antibodies against this protein were used to identify cDNA clones from a lambda gt11 expression library. Analysis of its cDNA sequence reveals high sequence similarity to three other 57 kd luminal endoplasmic reticulum proteins: protein disulfide isomerase, the beta-subunit of prolyl hydroxylase, and thyroid hormone binding protein. This finding suggests that the capacity to recognize multiple polypeptide domains may reside in a single luminal protein that participates in co- and/or posttranslational modifications of newly synthesized proteins.