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Electrostatic interactions across the dimer-dimer interface contribute to the pH-dependent stability of a tetrameric malate dehydrogenase |
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| Authors: | Bjørk Alexandra Mantzilas Dimitrios Sirevåg Reidun Eijsink Vincent G H |
| Affiliation: | a Department of Biology, University of Oslo, Box 1031 Blindern, N-0316 Oslo, Norway b Department of Biochemistry, University of Oslo, Box 1041 Blindern, N-0316 Oslo, Norway c Department of Chemistry and Biotechnology, Agricultural University of Norway, Box 5040, N-1432 Ås, Norway |
| Abstract: | Malate dehydrogenase (MDH) from the moderately thermophilic bacterium Chloroflexus aurantiacus (CaMDH) is a tetrameric enzyme, while MDHs from mesophilic bacteria usually are dimers. Using site-directed mutagenesis, we show here that a network of electrostatic interactions across the extra dimer-dimer interface in CaMDH is important for thermal stability and oligomeric integrity. Stability effects of single point mutations (E25Q, E25K, D56N, D56K) varied from −1.2°C to −26.8°C, and depended strongly on pH. Gel-filtration experiments indicated that the 26.8°C loss in stability observed for the D56K mutant at low pH was accompanied by a shift towards a lower oligomerization state. |
| Keywords: | Malate dehydrogenase Oligomerization Thermal stability Electrostatic interactions |
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