Recovery and Reusability of ApoUnaG Fluorescence Protein from the Unconjugated Bilirubin Complex Structure

This study is the first report on the separation and reusability of ApoUnaG protein, indicating excellent fluorescence response with high affinity and specificity toward unconjugated bilirubin (UC-BR) molecules, from the UnaG-UC-BR complex structure. The fluorescence properties of the UnaG-UC-BR complex (holo-UnaG) are studied by addition of different metal ions to perform possible interactions with holo-UnaG through absorbance and emission spectra. After addition of metal ions, some changes with respect to the type of metal ions are observed in fluorescence intensity of the holo-UnaG. When compared to metal ions, an excellent quenching response is sighted in the presence of Cu²⁺ ions by binding with UC-BR in the UnaG-UC-BR complex structure. Obtained non-fluorescence holo-UnaG-Cu²⁺ complex mixture is passed through Ni-NTA agarose to remove the ingredients such as Cu²⁺, UC-BR and Cu²⁺-UC-BR coordination complex from holo-UnaG. From the obtained experiments, it is concluded that Cu²⁺ ion can be used as an agent for the recovery of ApoUnaG protein via binding with UC-BR molecules. Graphical Abstract Recovery and Reusability of ApoUnaG Fluorescence Protein from the Unconjugated Bilirubin Complex Structure.