The effect of micro-environment on luminescence of aequorin: The role of amino acids and explicit water molecules on spectroscopic properties of coelenteramide

Despite the fact that the luminescence reaction mechanism of aequorin has been intensively investigated, details in luminescence such as the effect of important amino acids residues and explicit water molecules on spectroscopic properties of coelenteramide remain unclear. In this work, the effect of amino acids residues His16, Tyr82, Trp86, Phe113, Trp129, Tyr132, explicit water molecules Wat505 and Wat405 on the spectral properties of CLM− has been studied by CAM-B3LYP, TD M06L and TD CAM-B3LYP methods in hydrophobic environment and aqueous solution. In hydrophobic environment, the amino acids or water molecules have no significant effect on the absorption. Tyr82 and Trp86 move close to CLM− changes the hydrogen bond network, and thus, the spectral properties is significantly affected by the hydrogen bonds between His16H++Tyr82 + Trp86 and CLM−. Tyr82, Trp86 hydrogen bonding to CLM− upshifts the excited energy and helps emission spectra shift to blue region. Therefore, it is concluded that His16H++Tyr82 + Trp86 modify the emission spectra. The molecular electrostatic potential indicated that the greater electron density is located at the oxygen atom of 6-p-hydroxyphenyl group of CLM−, and it facilitates the formation of hydrogen bond with His16H++Tyr82 + Trp86. It is a critical condition for the modification of emission spectra. It is expected to help to understand the interactions between emitter and amino acids in the micro environment.