High solubility supports efficient refolding of thermally unfolded β-lactamase

Fusion technology is widely used to enhance soluble expression of recombinant proteins. We have shown before that halophilic β-lactamase (BLA) is an ideal candidate as a fusion partner. Here we have examined its thermal unfolding and refolding as a function of salt concentration. The thermal stability significantly increased as the salt concentration was increased from 0.2 to 1.84 M. Conversely, while reversibility of thermal unfolding was high at least up to 0.65 M salt, it was largely lost at 1.84 M. This was due to aggregation of thermally unfolded BLA. The addition of 3 M urea suppressed aggregation, which in turn resulted in restoration of reversible refolding of heat-denatured protein.