AVS 47th International Symposium
    Biomaterial Interfaces Wednesday Sessions
       Session BI+SS-WeM

Paper BI+SS-WeM8
A Fundamental Approach to Protein Adsorption: Changes in Free Energy for Adsorption of Individual Peptidyl Residues onto Functionalized SAM Surfaces

Wednesday, October 4, 2000, 10:40 am, Room 202

Session: Water at Biointerfaces
Presenter: R.A. Latour, Clemson University
Authors: R.A. Latour, Clemson University
L.L. Hench, Imperial College, UK
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Cellular response to biomaterial surfaces has great importance for the design of bioactive substrates for implant, drug delivery, and tissue engineering applications and is greatly influenced by protein/surface adsorption. All proteins are made up of amino acids (peptidyl residues); thus protein adsorption must be fundamentally governed by the submolecular interactions between a protein's residues and surface functional groups. The objective of this research was to develop an approach to quantitatively determine changes in Gibbs free energy for individual mid-chain residue/surface (R/S) functional group interactions and apply it to selected R/S group pairs. Molecular models (MOPAC/COSMO; CAChe software, Oxford Molecular Inc.) were created of 3 residues (Ala, Ser, Lys) and 3 SAM surfaces (CH@sub 3@, OH, COO-) to represent hydrophobic, hydrophilic, and charged systems in an aqueous environment. Adsorption enthalpy for each R/S pair was determined by positioning the residues over the surfaces and calculating the system energy as they were sequentially separated from the surface. Additional enthalpy and entropy contributions due to water restructuring effects were estimated based on changes in solvent accessible surface area and experimental wetting data. This was combined with the modeling data to calculate the net @DELTA@G@sub ads@. Ala was predicted to tightly bind to the CH@sub 3@ surface with @DELTA@G@sub ads@ = -5.8 kcal/mol with Ser and Lys each having @DELTA@G@sub ads@ > 0. All 3 residues exhibited @DELTA@G@sub ads@ > 0 for adsorption to the OH surface. Lys was predicted to be attracted to the COO- surface with @DELTA@G@sub ads@ = -5.4 kcal/mol, but only through intervening water layers with a 5 - 7 Å surface separation distance. Ala and Ser had @DELTA@G@sub ads@ > 0 for their interaction with the COO- surface. Further work is planned to integrate this type of data to develop a universal model for predicting protein-surface adsorption behavior.