Thermodynamics and structure of a salmon cold active goose-type lysozyme

Atlantic salmon goose-type lysozyme (SalG) was previously shown to display features of cold-adaptation as well as renaturation following heat treatment. In this study differential scanning calorimetry (DSC) was carried out to investigate unfolding and potential refolding, while X-ray crystallography was used to study structural factors contributing to the temperature-related characteristics. The recombinant SalG has a melting temperature (Tm) of 36.8 °C under thermal denaturation conditions and regains activity after returning to permissive (low) temperature. Furthermore, refolding is dramatically reduced in solutions with high SalG concentrations, coupled with significant protein precipitation. The structural features of SalG closely resemble those of other g-type lysozymes. However, the N-terminal region of SalG is less anchored to the rest of the molecule due to the absence of disulphide bonds, thus, contributing significantly to the low Tm of SalG. The absence of disulphide bonds and the distribution of salt bridges may at the same time ease refolding leading to renaturation.