Those methods such as ��grow�� to build a suitable derivative that meets all the requirements. The protocol that was used in this study to design Lig 1 to target the 150-cavity falls under the category of fragment based ligand design and can be applied to other systems as well. The DMXAA dynamics of the 150-loop have been found to be critical in mediating drug-protein interactions and drug resistance. The open 150-cavity has become a new target for novel inhibitor design. In order to design and verify new ligands that can lock the 150-loop in an open conformation, a combination of multiple computational biology methods, including molecular docking, fragment linking and MD simulations have been applied. A fragment library was first screened on the 150-cavity, and 1-Pyrrolidinebutanoic acid,β-[3-(3,5-dimethyl-1H-pyrazol-1-yl)phenyl]-3-[2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl]-,(βS,3R)- (hydrochloride) biological activity fragments with extensive interactions with 09N1 based on docking scores were chosen. Then the selected candidates were linked with ZMR using LigBuilder. At the same time, the linked molecules were filtered based on a series of criteria. Finally, all the linked molecules were tested using MD simulations to see whether they could bind stably with the target protein. One ligand has been shown interact stably with 09N1 with high binding affinity. Extensive simulations were also performed on two additional small molecules, ZMR and ETT. ZMR served as a positive control while ETT was used as a negative control. Our simulation data showed that ZMR stably binds with the receptor. Although ETT was previously proposed to lock the open 150-loop, we showed that ETT actually bound 09N1 with low affinity. In fact, ETT dissociated from 09N1 in MD simulations. By monitoring the pair-wise force formed between ETT and 09N1, the dissociating path was discovered, with the derived hydrophobic group of ETT found to be incapable of maintaining favorable contacts with residues around the 150- loop. Based on these findings, we have concluded that maintaining strong interactions between the newly derived group and the residues around the 150-loop is of great importance in the scaffold modification method. We hope that this combined method and the newly designed derivatives that lock the 150-loop in an open conformation comprise useful contributions for designing novel inhibitors to combat the spread of influenza virus. The human imm
