Thiol-independent interaction of protein disulphide isomerase with type X collagen during intra-cellular folding and assembly (original) (raw)

Protein disulphide isomerase (PDI) has been shown to be a multifunctional protein capable of catalysing disulphide-bond formation and isomerization, and of participating as a non-catalytic subunit of prolyl 4-hydroxylase (P4-H) and microsomal triacylglycerol transfer protein. It has also been proposed to function as a molecular chaperone during the refolding of denatured proteins in vitro. To investigate its potential role as a molecular chaperone within a cellular context, we studied the folding, modification and assembly of type X collagen in semi-permeabilized cells. Using this approach, we demonstrate that depletion of ATP has no effect on the rate or extent of helix formation, indicating that the individual triple helical regions do not interact with the molecular chaperone immunoglobulin heavy-chain binding protein (BiP). However, PDI was shown to interact transiently with type X during helix formation in a role related to its function as the beta subunit of P4-H. Once the col...