Titanium binding dodecapeptides and the impact of water structure

Molecular dynamics simulations on two peptides TiOBP1 (RPRGFGMSRERQ) and TiOBP2 (WFCLLGCDAGCW) adsorbing on flat and rough rutile (100) TiO2 surfaces in water are reported. Numerous contact points between charged side chains and the hydroxylated surfaces are formed with average energies of 60 and 90 kJ/mol for TiOBP1 and TiOBP2, respectively. The polar double contact points formed by adjacent positive and negative side chains immobilize the peptides on the surface more efficient than the single ones. The respective energies are around 230 kJ/mol and have values between those for hydrogen and covalent bonds. rface charge is tuned by using hydroxyl groups with formal charges and with point charges equal to those in the TIP3P water model. This has influence on the mobility of water in rigid layers on the surface. Peptides have to perforate these layers before adsorbing directly to the surface. This is favored by similarities in the charge distributions in side chains of polar residues with that of water. In earlier work, adsorption on top of the rigid layers rather than directly on the surface was found. We show that this effect depends on the mobility of the water in these layers and thus on the surface model.