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Enthalpy-entropy compensation at play in human copper ion transfer
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Pernilla Wittung-Stafshede)
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Gerhard Gröbner)
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Pernilla Wittung-Stafshede)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Copper (Cu) is an essential trace element but toxic in free form. After cell uptake, Cu is transferred, via direct protein-protein interactions, from the chaperone Atox1 to the Wilson disease protein (WD) for incorporation into Cu-dependent enzymes. Cu binds to a conserved C1XXC2 motif in the chaperone as well as in each of the cytoplasmic metal-binding domains of WD. Here, we dissect mechanism and thermodynamics of Cu transfer from Atox1 to the fourth metal binding domain of WD. Using chromatography and calorimetry together with single Cysto-Ala variants, we demonstrate that Cu-dependent hetero-protein complexes require the presence of C1 but not C2. Comparison of thermodynamic parameters for mutant versus wild type reactions reveals that the wild-type reaction involves strong entropy-enthalpy compensation. This property is explained by a dynamic inter-conversion of Cu-Cys coordinations in the wild type ensemble and may provide functional advantage by protecting against Cu mis-ligation and bypassing enthalpic traps.

Keyword [en]
copper chaperone, Atox1, Wilson disease protein, metal transport, size exclusion chromatography, thermodynamics, calorimetry
National Category
Biophysics Biochemistry and Molecular Biology Inorganic Chemistry
Research subject
URN: urn:nbn:se:umu:diva-100509OAI: diva2:792402

accepted at Scientific Reports, no DOI yet.

Available from: 2015-03-03 Created: 2015-03-03 Last updated: 2015-03-04Bibliographically approved
In thesis
1. Human copper ion transfer: from metal chaperone to target transporter domain
Open this publication in new window or tab >>Human copper ion transfer: from metal chaperone to target transporter domain
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many processes in living systems occur through transient interactions among proteins. Those interactions are often weak and are driven by small changes in free energy. Due to the short-living nature of these interactions, our knowledge about driving forces, dynamics and structures of these types of protein-protein heterocomplexes are though limited. This is especially important for cellular copper (Cu) trafficking:

Copper ions are essential for all eukaryotes and most bacteria. As a cofactor in many enzymes, copper is especially vital in respiration or detoxification. Since the same features that make copper useful also make it toxic, it needs to be controlled tightly. Additionally, in the reducing environment of the cytosol, Cu is present as insoluble Cu(I). To circumvent both toxicity and solubility issues, a system has evolved where copper is comforted by certain copper binding proteins, so-called Cu-chaperones. They transiently interact with each other to distribute the Cu atoms in a cell. In humans, one of them is Atox1. It binds copper with a binding site containing two thiol residues and transfers it to other binding sites, mostly those of a copper pump, ATP7B (also known as Wilsons disease protein).

My work was aimed at understanding copper-mediated protein-protein interactions on a molecular and mechanistic level. Which amino acids interact with the metal? Which forces drive the transfer from one protein to the other? Using biophysical and biochemical methods such as chromatography and calorimetry on wild type and point-mutated proteins in vitro, we found that the copper is transferred via a dynamic intermediate complex that keeps the system flexible while shielding the copper against other interactions.

Although similar transfer interactions can be observed in other organisms, and many conclusions in the copper field are drawn from bacterial and yeast analogs, we believe that it is important to investigate human proteins, too. Not only is their regulation different, but also only in humans we find the diseases linked to the proteins: Copper level regulation diseases are to be named first, but atypical copper levels have also been linked to tumors and amyloid dispositions. In summary, my observations and conclusions are of basic research character and can be of importance for both general copper and human medicinal research.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2015. 96 p.
copper homeostasis, copper chaperone, Atox1, ATP7B, Wilson disease protein, metal transport, size exclusion chromatography, thermodynamics, isothermal calorimetry
National Category
Inorganic Chemistry Biophysics Biochemistry and Molecular Biology
urn:nbn:se:umu:diva-100511 (URN)978-91-7601-203-1 (ISBN)
Public defence
2015-03-27, Lilla Hörsalen, KBC KB3A9, Umeå Universitet, Umeå, 10:00 (English)
Available from: 2015-03-06 Created: 2015-03-03 Last updated: 2015-03-27Bibliographically approved

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Niemiec, Moritz Sebastian
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