Circular dichroism and absorption spectroscopic data reveal binding of the natural cis-carotenoid bixin to human α1-acid glycoprotein

F. Zsila, Péter Molnár, J. Deli, Samuel F. Lockwood

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Using circular dichroism (CD) and electronic absorption spectroscopy techniques, interaction of the natural dietary cis-carotenoid bixin with an important human plasma protein in vitro was demonstrated for the first time. The induced CD spectra of bixin obtained under physiological conditions (pH 7.4, 37°C) revealed its binding to the serum acute-phase reactant α1-acid glycoprotein (AGP), a member of the lipocalin protein family. Spectral features of the extrinsic Cotton effects of bixin suggested the inclusion of a single, chirally distorted ligand molecule into the asymmetric protein environment. Compared with the absorption spectra obtained in ethanol and benzene, the strong red shift of the main absorption peak of AGP-bound bixin indicated that the proposed binding site was rich in aromatic residues, and also suggested that hydrophobic interactions were involved in the binding. Using the data obtained from the CD titration experiments, the association constant (Ka = 4.5 × 105 M-1) and stoichiometry of the binding (0.15) were calculated. The low value of the stoichiometry was attributed to the structural polymorphism of AGP. To the authors' knowledge, the current study represents the first human lipocalin protein for which carotenoid binding affinity has been explored in vitro with these techniques.

Original languageEnglish
Pages (from-to)298-309
Number of pages12
JournalBioorganic Chemistry
Volume33
Issue number4
DOIs
Publication statusPublished - Aug 2005

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Carotenoids
Circular Dichroism
Glycoproteins
Dichroism
Lipocalins
Acids
Stoichiometry
Proteins
Acute-Phase Proteins
Benzene
Polymorphism
Titration
Absorption spectroscopy
Hydrophobic and Hydrophilic Interactions
Cotton
Blood Proteins
Absorption spectra
Spectrum Analysis
Ethanol
Binding Sites

Keywords

  • α-Acid glycoprotein
  • Bixin
  • Circular dichroism spectroscopy
  • cis-Carotenoid
  • Induced chirality
  • Lipocalin
  • Red shift

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Organic Chemistry
  • Drug Discovery

Cite this

Circular dichroism and absorption spectroscopic data reveal binding of the natural cis-carotenoid bixin to human α1-acid glycoprotein. / Zsila, F.; Molnár, Péter; Deli, J.; Lockwood, Samuel F.

In: Bioorganic Chemistry, Vol. 33, No. 4, 08.2005, p. 298-309.

Research output: Contribution to journalArticle

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