Roles of trehalose and magnesium sulfate on structural and functional stability of firefly luciferase

Firefly luciferase is widely used in many analytical techniques. However, the enzyme is unstable, so that its relative inactivation results in low sensitivity of those techniques. In this study, we have investigated the effects of MgSO4 and trehalose on the structural stability and function of luciferase from Photinus pyralis using circular dichroism (CD), conventional and stopped-flow fluorescence spectroscopy and bioluminescence assay. The secondary structural content, compactness and its melting temperature are also studied, which showed that the stability of luciferase increased in the presence of additives. Measurements of refolding rate constants under conditions that favor folding, show that MgSO4 accelerates the folding of enzyme, on the contrary, refolding rate constant decreases in the presence of trehalose which can be attributed to its high viscosity. Finally, combined with remaining activity assay we concluded that magnesium sulfate and trehalose can be used for short- and long-term stabilization, respectively.