title: Differences in binding behavior of (-)-epigallocatechin gallate to β-lactoglobulin heterodimers (AB) compared to homodimers (A) and (B).
abstract: The lipocalin β-lactoglobulin (β-LG) exists in different natural genetic variants--of which β-LG A and B are predominant in bovine milk. At physiological conditions the protein dimerizes--building homodimers of β-LG A and β-LG B and heterodimers of β-LG AB. Although β-LG is one of the most intensely characterized lipocalins, the interaction behavior of ligands with hetero- and homodimers of β-LG is largely unknown. The present findings revealed significant differences for hetero- and homodimers regarding ligand binding capacity as tested with a model ligand (i.e. surface binding (-)-epigallocatechin gallate (EGCG)). These findings were confirmed using FT-IR, where the addition of EGCG influenced the β-sheet backbone of homodimer A and B with significantly higher intensity compared to heterodimer AB. Further, shape analysis by SAXS revealed oligomerization of both types of dimers upon addition of EGCG; however, homodimer A and B produced significantly larger aggregates compared to the heterodimer AB. In summary, the present study revealed that EGCG showed significantly different interaction reactivity (binding sites, aggregation size and conformational changes) to the hetero and homodimers of β-LG in the order β-LG A > B > AB. The results suggest that conformational differences between homodimers and heterodimers strongly influence the EGCG binding ability. This may also occur with other polyphenols and ligands of β-LG and gives not only important information for β-LG binding studies, but may also apply for polymorphisms of other self-aggregating lipocalins.
authors.affiliation: Christian-Albrechts-University of Kiel, Institute of Human Nutrition and Food Science, Division of Food Technology, Kiel, Germany.
authors.forename: Julia K
authors.initials: JK
authors.lastname: Keppler
authors.affiliation: Max Rubner-Institut (MRI), Department of Safety and Quality of Milk and Fish Products, Kiel, Germany.
authors.forename: Dierk
authors.initials: D
authors.lastname: Martin
authors.affiliation: Helmholtz-Zentrum Geesthacht, Zentrum für Material- und Küstenforschung GmbH, Geesthacht, Germany.
authors.forename: Vasil M
authors.initials: VM
authors.lastname: Garamus
authors.affiliation: Christian-Albrechts-University of Kiel, Institute of Human Nutrition and Food Science, Division of Food Technology, Kiel, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Schwarz
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism*; D008024:Ligands; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology*; D055503:Protein Multimerization / Q000502:physiology*; D017433:Protein Structure, Secondary; D053838:Scattering, Small Angle; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D007782:Lactoglobulins; D008024:Ligands; D002392:Catechin; C045651:epigallocatechin gallate
keywords: beta-lactoglobulin; epigallocatechin gallate; heterodimer; homodimer; ligand binding; lipocalin; protein aggregation