Differences in binding behavior of (−)-epigallocatechin gallate to β-lactoglobulin heterodimers (AB) compared to homodimers (A) and (B)

• Published in: Journal of molecular recognition 2015-11, Vol.28 (11), p.656-666
• Main Authors: Keppler, Julia K., Martin, Dierk, Garamus, Vasil M., Schwarz, Karin
• Format: Article
• Language: English
• Subjects: Agglomeration; Animals; beta-lactoglobulin; Binding; Binding sites; Binding Sites - physiology; Catechin - analogs & derivatives; Catechin - chemistry; Catechin - metabolism; Cattle; epigallocatechin gallate; Gallates; Genetics; heterodimer; homodimer; Lactoglobulins - chemistry; Lactoglobulins - metabolism; ligand binding; Ligands; lipocalin; Milk - chemistry; Milk - metabolism; Polyphenols; protein aggregation; Protein Binding - physiology; Protein Multimerization - physiology; Protein Structure, Secondary; Proteins; Scattering, Small Angle; Spectroscopy, Fourier Transform Infrared - methods; X-Ray Diffraction - methods
• ISSN: 0952-3499; 1099-1352
• DOI: 10.1002/jmr.2480

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. Copyright © 2015 John Wiley & Sons, Ltd. The whey protein β‐Lactoglobulin exists in different genetic variants, of which A and B are predominant. At physiological pH, the protein dimerizes to homodimers (consisting of similar genetic variants A or B) or to heterodimers (with mixed genetic variants AB). The present study revealed that the polyphenol (–)‐epigallocatechin gallate 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.