Bioluminescence and kinetic aspects of double mutated aequorin variants

Aequorin as an old small calcium-sensitive photoprotein is a blue fluorescence protein which converts coelenterazine (a substrate) to coelenteramide with a flash type emission. The decay kinetics and emission properties of this protein can be changed using directed mutagenesis of crucial amino acid residue. In this work, we prepared three double mutants: Y82F/W86F, Y82F/D153G, and W86F/D153G. According to our results, it seems that presence of Y82F mutation results in shift of emission to longer wavelengths while the W86F mutation shifts the emission to shorter wavelengths. Furthermore, comparison of the variants for light half-life indicated decreased t1/2 for the two variants of Y82F/D153G and W86F/D153G. But in compared to wild type aequorin, the Y82F/W86F variant displayed a 2-fold increase of light half-life. On the other hand, the thermostability properties of double mutants confirmed that only Y82F/D153G variant of apoaequorin is higher stability than others. Also, the single W86F mutant reached the highest stability against thermal shock. Our data suggest that replacement of single or few point mutations in the binding pocket or active site of aequorin affects its bioluminescence and kinetic properties and so could be used for new reporter production of this photoprotein with the feasibility and limited substitutions.