(348f) The Investigation of Green Tea Catechin Binding to Keratins by Molecular Dynamics and Experimental Validation

Binding of small molecules to macromolecules of human bio-substrates regulates the sub-cellular disposition and the subject is fundamental to intestinal absorption of nutrients and drugs as well as transdermal permeation of cosmetics active ^{1, 2}. A number of studies have been reported on the binding properties of plant actives to bio-substrate proteins, using various experimental techniques ^3-6. The knowledge of how active molecules bind to proteins at the molecular level is still limited. Molecular Dynamics (MD) simulations provide an alternative approach to understand the interaction between active molecules and biological substrates at the atomic level. MD simulations allow researchers to extract the most detailed information about the interactions between proteins and ligands and extracted information can be validated by experiments.

This study reports recent progresses in using MD simulations to investigate the thermodynamic and equilibrium properties of small molecule binding to macromolecules of human substrates using keratin-polyphenol as an example. The small molecule is epigallocatechin-3-gallate (EGCG), which is the most active polyphenol found in green tea and reported to have antioxidant and antimutagenic properties as an active compound ⁷. Keratin 1 and keratin 10, the most abundant SC keratins, have been chosen as the biosubstrate. The umbrella sampling technique together with the weighted histogram analysis method are used to calculate the binding free energy of EGCG to different keratin segments (α-helical rod, coiled coil of α-helixes and unstructured terminals). The influence of various conditions of temperature, salt concentration, EGCG/keratin molar ratio on the binding free energy and the number of hydrogen bonds between different protein segments and ligand has been assessed. Results have been also obtained on protein conformational shifts and the solvent accessible surface area changes in the presence of EGCG.  It is shown that EGCG binding to keratin segments is driven by hydrophobic interaction involving the aromatic attraction and hydrogen bonding. EGCG molecule has 8 hydrogen donors and 11 hydrogen acceptors. It can form hydrogen bonds with both hydrophilic and hydrophobic residues of keratin proteins. The strongest keratin-EGCG interaction is found to be with the aromatic residues of keratin terminals and helical rod. The results from MD simulations are in a good agreement with fluorescence quenching and Isothermal Titration Calorimetry (ITC) experiments. Based on the results of both computer simulation and experiment, a new insight into EGCG-keratin interactions has been gained.

Keywords: EGCG, Stratum Corneum, Keratin, Binding free energy, Molecular Dynamics, Polyphenols

References

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