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Title: Molecular characterisation of PDIp : the pancreas-specific isoform of PDI
Author: Walker, Kelly L.
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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PDIp is a close homolog of the well known protein folding catalyst PDI. Unlike PDI however, PDIp exhibits restricted protein expression and is found predominantly in the exocrine pancreas. Currently, the physiological function of PDIp is unknown but previous work has shown a clear specificity for substrates containing a hydroxyaryl group. Again this is in contrast to PDI which exhibits more general specificity. This work to investigate the in vitro activities of PDIp, was stimulated by the hypothesis that PDIp has an essential role in folding a specific subset of secretory proteins. The identity of these proteins is currently unknown. In this work, the redox-mediated conformational changes of PDIp have been studied and compared using far UV CD, dynamic light scattering and limited proteolysis. Compared to PDI, these changes are conservative in PDIp. Also, unlike PDI for which b’xa’c is the minimal redox-active cassette, the PDIp a and b domains seem to be involved in modulating these conformational changes. This may indicate that PDIp has a unique substrate binding mechanism that may work synergistically with its restricted substrate specificity. Using the insulin reduction assay, PDIp was shown to have ~50% of the oxidoreductase activity of PDI and this was not due to the aberrant threonine residue in the a’ domain active site motif (CTHC). Further investigation by stopped flow kinetic studies showed that the low activity could be due to the abnormally high pKa for the PDIp a domain N-terminal catalytic cysteine. This result was unexpected because PDI and PDIp a share the same catalytic active site motif (CGHC) indicating that nearby residues may act as mediators of activity. Future work to clarify this will be essential. This is the first study of the structure of PDIp and its molecular basis for activity. Through investigation of these two areas, it is hoped that the general understanding of the role of PDIp and its contribution to oxidative folding in secretory tissues will be improved.
Supervisor: Not available Sponsor: Medical Research Council (MRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH301 Biology ; QP Physiology