Chapter 3. Outlines of the study

PDI is a multifunctional enzyme found in abundance in eukaryotic cells. It consists of four structurally independent domains which function in co-operation to catalyse the wide range of reactions PDI is capable of. It is known that PDI consists of two catalytically active domains (a and a’) and two catalytically inactive domains (b and b’). In addition, PDI has a C-terminal, highly acidic region c. Domain b’ has been assigned the role of being the primary peptide binding domain of PDI, but the function of domain b is still unclear.

In addition of having specific catalytic functions in the thiol-disulfide exchange of protein cysteines, PDI is a subunit in two known enzymes, one of which is collagen prolyl 4-hydroxylase (C-P4H). C-P4H is a crucial enzyme in collagen biosynthesis and the role of PDI in the C-P4H enzyme tetramer is essential for the formation and stability of a functional C-P4H.

The aims of this research were:

1. To study the roles of the individual domains and the c region of PDI in the formation and activity of the C-P4H enzyme tetramer and for the different catalytic activities of PDI.

2. To study whether the domains of ERp57, a member of the PDI family of proteins, could structurally complement any of those of PDI in the C-P4H subunit function or the peptide binding ability of PDI.

3. To characterize the peptide binding domain b’ in detail.