A new ligand for an old lipocalin: induced circular dichroism spectra reveal binding of bilirubin to bovine β‐lactoglobulin

FEBS Letters

Zsila, Ferenc¹ 

[1] Department of Molecular Pharmacology, Institute of Chemistry, Chemical Research Center, P.O. Box 17, 1525 Budapest, Hungary

关键词: β-Lactoglobulin;    Bilirubin;    Exciton coupling;    Induced chirality;    Lipocalin;    Molecular recognition;    BLG;    bovine β-lactoglobulin;    BR;    bilirubin;    CD;    circular dichroism;    CE;    Cotton effect;    DMSO;    dimethyl sulfoxide;    L/P;    ligand/protein molar ratio;    mdeg;    millidegree;    UV/Vis;    ultraviolet–visible;   

DOI  :  10.1016/S0014-5793(03)00203-5

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

This study reports that bilirubin–bovine β-lactoglobulin (BLG) complexes exhibit very characteristic induced circular dichroism (CD) spectra in the visible absorption region. Due to intramolecular chiral exciton coupling between the dipyrrinone chromophores, the long-wavelength negative and short-wavelength positive CD bands clearly prove that a single bilirubin molecule binds to BLG in a left-handed helical conformation (in pH 7.4 phosphate buffer Δϵ _min is −54 M⁻¹ cm⁻¹ at 467 nm and Δϵ _max is +48.5 M⁻¹ cm⁻¹ at 412 nm). The very low aqueous solubility and strong tendency of bilirubin molecules to aggregate around pH 7.4 meant that much more intense CD bands were measured at alkaline pH values owing to the increasing solubility of the ligand. Vanishing CD activity obtained upon titration of the complex with palmitic acid known to bind in the hydrophobic cavity of BLG indicates bilirubin to be bound at the open end mouth of the β-barrel. Reversible changes of the induced CD spectrum due to acidic pH shift of the sample solution lead to the same conclusion.

【 授权许可】

Unknown