Interactions between flavan-3-ols and poly(L-proline) studied by isothermal titration calorimetry: effect of the tannin structure

J Agric Food Chem. 2007 Oct 31;55(22):9235-40. doi: 10.1021/jf071297o. Epub 2007 Sep 12.

Abstract

Interactions of proline-rich proteins (PRPs) with flavan-3-ols was studied using poly(L-proline) as a model protein by means of isothermal titration calorimetry (ITC). Several parameters were varied: (i) the galloylation and B-ring trihydroxylation of the flavan-3-ols (catechin, epicatechin, epicatechin gallate, and epigallocatechin gallate) and (ii) the degree of polymerization (monomers were compared to a mixture of oligomers with average degree of polymerization of 3.85). Large differences were observed between the flavan-3-ol monomers: no enthalpy change was measured when catechin and epicatechin were titrated by poly(L-proline), whereas thermodynamic parameters were determined in the case of galloylated monomers and mixture of oligomers. Stoichiometry ranged from 1 oligomer bound for each 12 proline units to 1 galloylated monomer for each 8 or 10 proline units. Association constants were in the range of 10(4)-10(5) M(-1), indicating a relatively high affinity of galloylated flavanols toward poly(L-proline), and the coexistence of both enthalpy- and entropy-driven phenomena was suggested. Finally, the binding of grape seed tannins to proteins was shown to be a cooperative process.

MeSH terms

  • Calorimetry*
  • Flavonoids / chemistry*
  • Gallic Acid / chemistry
  • Hydroxylation
  • Peptides / chemistry*
  • Tannins / chemistry*
  • Thermodynamics

Substances

  • Flavonoids
  • Peptides
  • Tannins
  • polyproline
  • flavan-3-ol
  • Gallic Acid