Abstract
Isocitrate dehydrogenase [IDH; EC 1.1.1.42] from the thermoacidophilic archaeon Thermoplasma acidophilum (TaIDH) showed high thermal stability with an apparent melting temperature, T m, of 82.2 and 84.5°C at pH 7.5 and 5.8, respectively. Based on structural alignment of TaIDH with IDH from Aeropyrum pernix (ApIDH) and Archaeoglobus fulgidus (AfIDH) residues forming an aromatic cluster in the clasp-domain thought to strengthen the dimer interface in ApIDH and AfIDH were identified in the former enzyme. Moreover, TaIDH had a shortened N-terminus that may protect the enzyme from thermal denaturation. The enzyme activity of TaIDH was highest at 70°C. The pH-activity profile was bell-shaped with an optimum shifted to a lower pH compared to AfIDH. The activity of TaIDH was influenced by changes in pH with a three-fold reduction in activity when the pH was shifted from the pH-optimum at 7.5 to pH 5.8. However, the specific activity at pH 5.8 was still high when compared with AfIDH. The reduction in activity at pH 5.8 was not due to instability of the enzyme as the T m of TaIDH was higher at pH 5.8 than at 7.5 and the enzyme retained 91% of its activity after incubation at 1 h at pH 5 and 60°C. The difference in the pH-profile of TaIDH in comparison with AfIDH may thus be related to the pK as of their catalytic residues involved in the initial proton abstraction and the final proton donation during the catalysis of oxidative decarboxylation of isocitrate to 2-oxoglutarate and reduced coenzyme.
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Abbreviations
- IDH:
-
Isocitrate dehydrogenase
- TaIDH:
-
Thermoplasma acidophilum IDH
- AfIDH:
-
Archaeoglobus fulgidus IDH
- PfIDH:
-
Pyrococcus furiosus IDH
- EcIDH:
-
Escherichia coli IDH
- DSC:
-
Differential scanning calorimetry
- T m :
-
Melting temperature
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Acknowledgments
This work was supported by the Norwegian Research Council (Project no. 153774/420). We are grateful to Dr. Aurora Martinez, Department of Biomedicine, University of Bergen, for access to her laboratory facilities and expertise in use of differential scanning calorimetry. The excellent laboratory skills of Lisbeth Glærum and Marit Steine Madsen are also much appreciated.
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Communicated by G. Antranikian.
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Stokke, R., Birkeland, NK. & Steen, I.H. Thermal stability and biochemical properties of isocitrate dehydrogenase from the thermoacidophilic archaeon Thermoplasma acidophilum . Extremophiles 11, 397–402 (2007). https://doi.org/10.1007/s00792-006-0045-y
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DOI: https://doi.org/10.1007/s00792-006-0045-y