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Thermodynamic Characterization of the Interaction between the C-Terminal Domain of Extracellular Superoxide Dismutase and Heparin by Isothermal Titration Calorimetry
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Physics, Chemistry and Biology, Molecular Biotechnology . Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.ORCID iD: 0000-0002-4694-5611
2009 (English)In: BIOCHEMISTRY, ISSN 0006-2960, Vol. 48, no 41, 9932-9940 p.Article in journal (Refereed) Published
Abstract [en]

Extracellular superoxide dismutase (ECSOD) interacts with heparin through its C-terminal domain. In this study we used isothermal titration calorimetry (ITC) to get detailed thermodynamic information about the interaction. We have shown that the interaction between ECSOD and intestinal mucosal heparin (M-w 6000-30000 Da) is exothermic and driven by enthalpy at physiological salt concentration. However, the contribution from entropy is favorable for binding or small isolated heparin fragments. By studying different size-defined heparin fragments, we also concluded that it hexasaccharide moiety is sufficient for strong binding to ECSOD. The binding involves proton transfer from the buffer to the ECSOD-heparin complex, and the results indicate that the number of ionic interactions made between ECSOD and heparin upon binding varies from three to five for heparin and an octasaccharide fragment, respectively. Surprisingly and despite the many charges found oil both the protein and the polysaccharide, our results indicate that the nonionic contribution to the binding is large. From the temperature dependence we have calculated the constant pressure heat capacity change (Delta C-p) of the interaction to -644 J K-1 mol(-1) and -306 J K-1 mol(-1) for heparin and all octasaccharide, respectively

Place, publisher, year, edition, pages
2009. Vol. 48, no 41, 9932-9940 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-51398DOI: 10.1021/bi900981kOAI: diva2:274605
Available from: 2009-10-30 Created: 2009-10-30 Last updated: 2016-05-04
In thesis
1. Protein Engineering of Extracellular Superoxide Dismutase: Characterization of Binding to Heparin and Cellular Surfaces
Open this publication in new window or tab >>Protein Engineering of Extracellular Superoxide Dismutase: Characterization of Binding to Heparin and Cellular Surfaces
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Accumulating evidence indicates that oxygen free radicals are involved in many diseases and pathological conditions, such as aging, inflammation, reperfusion damage of ischemic tissue and various cardiovascular diseases. Extracellular superoxide dismutase (ECSOD) thus plays a major role in the maintenance of cells by providing protection against these toxic substances in the extracellular space. Various animal studies have shown that ECSOD has the ability to protect against many of these disorders, and interest has therefore evolved in the potential therapeutic use of the enzyme.

However, despite strenuous efforts, large-scale production of the enzyme has not been achieved. To overcome this problem, a mimic of the enzyme, PseudoECSOD, has previously

been constructed. This chimera is easy to produce in large amounts and has all the structural, enzymatic and heparin-binding characteristics of ECSOD, making it a potential substitute for ECSOD in therapeutic situations. However, the copper content of PseudoECSOD has been shown to be rather low, and since the copper ion is very important for the catalytic function of the enzyme, a production system that utilizes a copper chaperone for proper insertion of copper into the active site of the enzyme was constructed. The results show that the copper content of PseudoECSOD produced by this system is close to 100 %.

In order to use PseudoECSOD therapeutically, further investigations of its binding capability and protective properties are needed. Therefore, the binding of ECSOD and PseudoECSOD to heparin was investigated using isothermal titration calorimetry. The results show that although some purely ionic interactions are important for the binding between ECSOD and heparin, there is also a substantial contribution from non-ionic interactions. The investigation also showed that the C-terminal domain is the only part of ECSOD that contributes to productive binding, and that the binding of PseudoECSOD and ECSOD to heparin is similar.

In addition, analysis of mutant proteins strongly indicated that the amino acids R210, K211 and R214 are important for optimal binding of ECSOD to heparin, accounting for about 30 % of the total binding energy. The structural placement of these amino acids in an α-helix also confirms the hypothesis postulated by Margalit et al., that a common structural motif for heparin-binding proteins may be two positively charged amino acids at a distance of approximately 20 Å in the 3D-structure, facing opposite directions of a α-helix. The importance of these residues was also confirmed by analysis of a phage display library of the C-terminal domain of ECSOD.

The binding of PseudoECSOD to heparan sulfate on cell surfaces of two different cell types, HepG2 and endothelial cells, was also investigated. The results clearly show that PseudoECSOD binds to these cells in a very similar manner to ECSOD. To investigate the protective properties of PseudoECSOD against ischemia-reperfusion injuries, an isolated rabbit heart model was used. The results indicate that the enzyme has a protective effect. However, more experiments using the rabbit heart and other animal models are needed to identify the optimal dose for protective purposes. The protective properties of PseudoECSOD in human tissue should also be thoroughly investigated.

In summary, the findings in these studies, together with earlier results showing the close resemblance of PseudoECSOD to ECSOD in structural, enzymatic and heparin-binding properties, further support the proposition that PseudoECSOD may be a good substitute for ECSOD to use in therapeutic interventions.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 61 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1159
National Category
Natural Sciences
urn:nbn:se:liu:diva-52452 (URN)978-91-7393-473-2 (ISBN)
Public defence
2010-01-29, Berzeliussalen, Hälsouniversitetet, Campus Valla, Linköpings universitet, Linköping, 13:00 (English)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2016-05-04Bibliographically approved

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