Algorithmic Challenges in Structure-Based Drug Design and NMR Structural Biology

The three-dimensional structure of a biomolecule rather than its one-dimensional sequence determines its biological function. At present, the most accurate structures are derived from experimental data measured mainly by two techniques: X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy. Because neither X-ray crystallography nor NMR spectroscopy could directly measure the positions of atoms in a biomolecule, algorithms must be designed to compute atom coordinates from the data. One salient feature of most NMR structure computation algorithms is their reliance on stochastic search to find the lowest energy conformations that satisfy the experimentally-derived geometric restraints. However, neither the correctness of the stochastic search has been established nor the errors in the output structures could be quantified. Though there exist exact algorithms to compute structures from angular restraints, similar algorithms that use distance restraints remain to be developed. An important application of structures is rational drug design where protein-ligand docking plays a critical role. In fact, various docking programs that place a compound into the binding site of a target protein have been used routinely by medicinal chemists for both lead identification and optimization. Unfortunately, despite ongoing methodological advances and some success stories, the performance of current docking algorithms is still data-dependent. These algorithms formulate the docking problem as a match of two sets of feature points. Both the selection of feature points and the search for the best poses with the minimum scores are accomplished through some stochastic search methods. Both the uncertainty in the scoring function and the limited sampling space attained by the stochastic search contribute to their failures. Recently, we have developed two novel docking algorithms: a data-driven docking algorithm and a general docking algorithm that does not rely on experimental data. Our algorithms search the pose space exhaustively with the pose space itself being limited to a set of hierarchical manifolds that represent, respectively, surfaces, curves and points with unique geometric and energetic properties. These algorithms promise to be especially valuable for the docking of fragments and small compounds as well as for virtual screening.