Interactions between flavan-3-ols and poly(L-proline) studied by isothermal titration calorimetry: effect of the tannin structure.
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.
Poncet-Legrand
Céline
C
UMR1083 Sciences pour l'Knologie, INRA, Université Montpellier 1, France. celine.poncet@supagro.inra.fr
Gautier
Catherine
C
Cheynier
Véronique
V
Imberty
Anne
A
D002151:Calorimetry; D005419:Flavonoids / Q000737:chemistry*; D005707:Gallic Acid / Q000737:chemistry; D006900:Hydroxylation; D010455:Peptides / Q000737:chemistry*; D013634:Tannins / Q000737:chemistry*; D013816:Thermodynamics
D005419:Flavonoids; D010455:Peptides; D013634:Tannins; C011083:polyproline; C404987:flavan-3-ol; D005707:Gallic Acid