title: Size and molecular flexibility affect the binding of ellagitannins to bovine serum albumin.
abstract: Binding to bovine serum albumin of monomeric (vescalagin and pedunculagin) and dimeric ellagitannins (roburin A, oenothein B, and gemin A) was investigated by isothermal titration calorimetry and fluorescence spectroscopy, which indicated two types of binding sites. Stronger and more specific sites exhibited affinity constants, K1, of 10(4)-10(6) M(-1) and stoichiometries, n1, of 2-13 and dominated at low tannin concentrations. Weaker and less-specific binding sites had K2 constants of 10(3)-10(5) M(-1) and stoichiometries, n2, of 16-30 and dominated at higher tannin concentrations. Binding to stronger sites appeared to be dependent on tannin flexibility and the presence of free galloyl groups. Positive entropies for all but gemin A indicated that hydrophobic interactions dominated during complexation. This was supported by an exponential relationship between the affinity, K1, and the modeled hydrophobic accessible surface area and by a linear relationship between K1 and the Stern-Volmer quenching constant, K(SV).
authors.affiliation: School of Agriculture, Policy and Development, University of Reading , Earley Gate, P.O. Box 236, Reading RG6 6AT, United Kingdom.
authors.forename: Marina A
authors.initials: MA
authors.lastname: Dobreva
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Green
authors.forename: Irene
authors.initials: I
authors.lastname: Mueller-Harvey
authors.forename: Juha-Pekka
authors.initials: JP
authors.lastname: Salminen
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: Howlin
authors.forename: Richard A
authors.initials: RA
authors.lastname: Frazier
mesh_terms: D001665:Binding Sites; D002151:Calorimetry; D019277:Entropy; D047348:Hydrolyzable Tannins / Q000737:chemistry* / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D015394:Molecular Structure; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013634:Tannins / Q000032:analysis / Q000737:chemistry
chemical_list: D047348:Hydrolyzable Tannins; D013634:Tannins; D012710:Serum Albumin, Bovine
keywords: ellagitannins; fluorescence; hydrophobic accessible surface area; isothermal titration calorimetry; molecular flexibility; molecular size