Baculovirus expression of two protein disulphide isomerase isoforms from Caenorhabditis elegans and characterization of prolyl 4-hydroxylases containing one of these polypeptides as their β subunit

Protein disulphide isomerase (PDI; EC 5.3.4.1) is a multifunctional polypeptide that is identical to the β subunit of prolyl 4-hydroxylases. We report here on the cloning and expression of the Caenorhabditis elegans PDI}β polypeptide and its isoform. The overall amino acid sequence identity and similarity between the processed human and C. elegans PDI}β polypeptides are 61% and 85% respectively, and those between the C. elegans PDI}β polypeptide and the PDI isoform 46% and 73%. The isoform differs from the PDI}β and ERp60 polypeptides in that its N-terminal thioredoxin-like domain has an unusual catalytic site sequence -CVHC-. Expression studies in insect cells demonstrated that the C. elegans PDI}β polypeptide forms an active prolyl 4-hydroxylase α # β # tetramer with the human α subunit and an αβ dimer with the C. elegans α subunit, whereas the C. elegans PDI isoform formed no prolyl 4-hydroxylase with either