Reversible thermal unfolding of Bacillus subtilis levansucrase is modulated by Fe3+ and Ca2+

The equilibrium transition curves for thermal unfolding of levansucrase were established at several pH values. At pH 7 and within the temperature range of bacterial growth, the unfolded form is predominant. However, under such conditions, refolding is promoted by the only addition of Ca2+ or Fe3+. We propose that the tertiary structure flexibility of levansucrase plays a key role in its secretion process.