Intersubunit salt bridges with a sulfate anion control subunit dissociation and thermal stabilization of Bacillus sp.  TB-90 urate oxidase (BTUO) is 45 °C, but this enzyme is one of the most thermostable urate oxidases.  A marked increase (>10 °C) in its thermal stability is induced by high concentrations (0.8–1.2 M) of sodium sulfate.  Calorimetric measurements and size exclusion chromatographic analyses suggested that sulfate-induced thermal stabilization is related to the binding of a sulfate anion that repressed the dissociation of BTUO tetramers into dimers.  The network of charged hydrogen bonds via the bound sulfate is suggested to contribute significantly to the thermal stabilization of both subunit dimers and the tetrameric assembly of BTUO.  Knowledge of the mechanism of salt-induced stabilization will help to develop new strategies for enhancing protein thermal stabilization.
THERM