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Evaluation of Luciferase Thermal Stability by Arginine Saturation in the Flexible Loops



The firefly luciferase enzyme is widely used in protein engineering and diverse
areas of biotechnology, but the main problem with this enzyme is low-temperature stability. Previous
reports indicated that surface areas of thermostable proteins are rich in arginine, which increased
their thermal stability. In this study, this aspect of thermophilic proteins evaluated by mutations of surface
residues to Arg. Here, we report the construction, purification, and studying of these mutated luciferases.



For mutagenesis, the QuikChange site-directed mutagenesis was used and the I108R,
T156R, and N177R mutant luciferases were created. In the following, the expression and purification
of wild-type and mutant luciferases were conducted and their kinetic and structural properties were analyzed.
To analyze the role of these Arg in these loops, the 3D models of these mutants’ enzymes were
constructed in the I-TASSER server and the exact situation of these mutants was studied by the
SPDBV and PyMOL software.



Overall, the optimum temperature of these mutated enzymes was not changed. However, after
30 min incubation of these mutated enzymes at 30°C, the I108R, T156R, N177R, and wild-type kept the
80%, 50%, 20%, and 20% of their original activity, respectively. It should be noted that substitution of
these residues by Arg preserved the specific activity of firefly luciferase.



Based on these results, it can be concluded that T156R and N177R mutants by compacting
local protein structure, increased the thermostability of luciferase. However, insertion of positively
charged residues in these positions create the new hydrogen bonds that associated with a series of
structural changes and confirmed by intrinsic and extrinsic fluorescence spectroscopy and homology
modeling studies.
