However as the initial screening involved an enormous number

However as the ZM241385 initial screening involved an enormous number of compounds it was important to start the docking simulations using a representative target structure. This was done to reduce the computational cost without losing significant information related to the target flexibility. Focusing on the binding site, Figure 1 represents the RMSD of the relaxed 9 NMR conformations compared to the 10th structure. We selected the centroid of the 9 structures to be our initial target. That is, we started the docking procedure using a binding site that has an equal RMSD separation from the other targets. The RMSD values ranged from 0.10 nm to 0.28 nm. Only two conformations were significantly separated from the reference conformation. Based on that, we choose conformation 4, with an RMSD separation of 0.21 nm to be our representative target. The rest of the structures were used in re-docking of the top 2,000 hits obtained from the initial single-target screening. The second stage was a more rigorous docking approach that buy CPDA employed the RCS methodology. In the RCS approach, allatom MD simulations are applied to explore the conformational space of the target, while docking is subsequently used for the fast screening of drug libraries against an ensemble of receptor conformations. This ensemble is extracted at predetermined time intervals from the simulation, resulting in hundreds of thousands of protein conformations. Each conformation is then used as a target for an independent docking experiment. The RCS methodology has been successfully applied to a number of cases. An excellent example is that of an HIV inhibitor, raltegravir which became the first FDA approved drug targeting HIV integrase,. Other successful examples include the identification of novel inhibitors of the acetylcholine binding protein, RNA-editing ligase 1, the influenza protein neuraminidase and Trypanosoma brucei uridine diphosphate galactose 49-epimerase. These applications employed alternative ways to solve two main problems with the method, namely, reducing the number of extracted target conformations and deciding on how to select the final set of hits after carrying out the screening process. For the first problem, a number of studies suggested extracting t