Submitted to the faculty of the University Graduate School in partial fulfillment of the requirements for the degree Master of Science in the School of Informatics, Indiana University December 2005 / The approach of exploiting highly conserved protein folds and structure in understanding protein function and in designing drugs leads to drugs that are less selective due to association with similar proteins. Over the years an open problem for researchers has been to develop drug design models based on non-conserved features to have higher selectivity. Recently a new structural feature, the dehydron, has been demonstrated to vary across proteins with conserved folds. Dehydrons are backbone hydrogen bonds that are not adequately protected from water. The importance of wrapping dehydrons in ligand binding and non-conservation of dehydrons across similar proteins makes them important candidates for markers in drug design. Investigation on a series of proteins – PDB entries: 1IA8, 1NVQ, 1NVS, 1NVR, 1OKZ, and 1PKD – revealed the potential impact of wrapping on binding affinity of the ligands. Unlike in 1NVS, 1NVR, 1OKZ, and 1PKD, inhibitor UCN in 1NVQ wrapped both the dehydrons in active site region of the checkpoint protein kinase, thereby indicating an increased potency and higher selectivity. On detailed analysis of 193 protein kinases, roughly 70% were found to have two or more dehydrons in the neighborhood of the bound ligand. Also, about 70% of proteins had dehydrons within the active site region. Only around 20% of ligands, however, actually wrapped two or more dehydrons. These statistics clearly illustrate the significance of dehydrons and their potential use as markers for drug design to enhance drug efficacy as well as selectivity, and to reduce side effects in the process.

A dehydrogen is an ‘under-wrapped’ hydrogen bond in a protein that is purported to be a hot spot for binding due to the favorable replacement of water with hydrocarbon upon binding of another protein. A model at the level of dielectric constants is used to test the validity of the claim that moving a hydrogen bond from high dielectric (i.e. a dehydron) to low dielectric (i.e. after binding of another protein) is actually a thermodynamically favorable process. In simulation, several proteins have been shown to undergo a dewetting transition when fixed components are separated a small distance. A new atomic-level hydrophobicity scale is combined with topographical information to characterize protein interfaces. The relationship between hydrophobicity and topography for protein surfaces known to be involved in binding is examined. This framework is then applied to identify surface characteristics likely to have an affect on the occurrence of a dewetting transition. Cadmium selenide (CdSe) nanoparticles form nanospheres or nanorods when grown in solutions of varying concentrations of the surfactants hexylphosphonic acid (HPA) and trioctylphosphine oxide (TOPO). Relative binding free energies are calculated for HPA and TOPO to the solvent-accessible faces of CdSe crystals. Binding free energies calculated with a Molecular Mechanics-Generalized Born model are used to identify a set of low free energy structures for which the solvation free energy is refined with the solution to the Poisson equation. These relative binding free energies provide information about the relative growth rates of these crystal faces in the presence of surfactants. Relative growth rates are then used to help understand why nanoparticles form certain shapes in the presence of specific surfactants. / text