Date of Award
Doctor of Philosophy
Dr. David Huffman
Dr. James Kiddle
Dr. Wendy D. Ransom-Hodgkins
Dr. Ekkehard Sinn
The Wilson protein (ATP7B) is a copper transporting ATPase that is involved in copper trafficking and homeostasis. Unlike the other known P-type ATPases, it possesses six homologous metal binding domains at the N-terminal end. Several mutations in the gene coding for this protein lead to Wilson disease, a hepatic disorder characterized by impaired excretion of copper in the bile, and accumulation of copper in body organs such as the liver, brain, kidney, and eye cornea. Characterization of various regions of expressed and purified ATP7B has been hampered by its low stability, aggregation and degradation.
In this research, novel methods were developed to express and purify stable N-terminal copper binding domains (MBDs), a 577 amino acid construct. These domains were characterized by Gel Filtration, Light Scattering and Circular Dichroism. The results indicate that the domains are polydisperse and have a larger hydrodynamic radius relative to a globular protein of the same molecular mass.
Y532H, a novel disease-causing mutation in domains 5 and 6 of the Wilson protein was also expressed. WD5-6(Y532H) could not be purified by established protocols. Therefore, it was purified using two different methods: (1) insoluble recombinant inclusion bodies were extracted and a procedure was developed to purify the refolded fusion protein and (2) a lower temperature procedure was developed to express soluble non-fusion recombinant protein. The WD5-6(Y532H) protein was characterized by Gel Filtration, Light Scattering, Circular Dichroism and Nuclear Magnetic Resonance. The results reveal that the Y532H mutation does not affect the overall structural organization of the native WD5-6 and the conformational stability of the protein. However, the NMR data of the WD5-6(Y532H) recovered by refolding reveals structural perturbations in the area around the mutation.
This work represents advances in the understanding of the function of the N-terminal region of the Wilson protein (ATP7B). The purification methods and strategies, key findings, and new developments presented in this work will be helpful not only to the individuals working in this field, but also to the scientific community at large.
Muia, Joshua Mutambuki, "Characterization of the N-Terminal Domains and Disease-Causing Mutations of the Human Wilson Protein" (2010). Dissertations. 609.