Induced chirality upon binding of cis-parinaric acid to bovine β-lactoglobulin: Spectroscopic characterization of the complex

TitleInduced chirality upon binding of cis-parinaric acid to bovine β-lactoglobulin: Spectroscopic characterization of the complex
Publication TypeJournal Article
Year of Publication2002
AuthorsZsila, F, Imre, T, Szabó, PT, Bikádi, Z, Simonyi, M
JournalFEBS Letters
Volume520
Issue1-3
Pagination81 - 87
Date Published2002
KeywordsBovine β-lactoglobulin, Circular dichroism spectroscopy, cis-Parinaric acid, Induced chirality, Ligand binding, Mass Spectrometry
Abstract

Binding of the polyunsaturated cis-parinaric acid to bovine β-lactoglobulin (BLG) was studied by circular dichroism (CD), electronic absorption spectroscopy and mass spectrometry methods. Upon protein binding, the UV absorption band of parinaric acid is red shifted by ca. 5 nm, showing hypochromism and reduced vibrational fine structure, suggesting that the ligand binds as a monomer in non-planar geometry. In the CD spectra measured at pH 7.36 and 8.5 a strong, negative Cotton band appears centered at 310 nm (Δε=-25 M-1 cm-1) corresponding to the long-wavelength absorption band of cis-parinaric acid. The source of this induced optical activity is the helical distortion of the polyene chromophore caused by the chiral protein environment. From CD spectral data the value of the association constant was calculated to be 4.7×105 M-1 at pH 7.36. CD and mass spectrometry measurements showed that parinaric acid binds weakly to BLG in acidic solution, though small peaks at mass 18559 and 18645 can be obtained in the reconstructed electrospray mass spectrum; these correspond to the binding of parinaric acid in 1:1 stoichiometry to both monomer variants of BLG B and A. The hydrophobic interior cavity of BLG was assigned as the primary binding site of cis-parinaric acid. © 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

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