Molecular basis of the interaction for an essential subunit PA-PB1 in influenza virus RNA polymerase: insights from molecular dynamics simulation and free energy calculation.

The emergence of the extremely aggressive influenza recently has highlighted the urgent need for new effective treatments. The influenza RNA-dependent RNA polymerase (RdRp) heterotrimer including PA, PB1 and PB2 has crucial roles in viral RNA replication and transcription. The highly conserved PB1 binding site on PA can be considered as a novel potential drug target site. The interaction between PB1 binding site and PA is crucial to many functions of the virus. In this study, to understand the detailed interaction profile and to characterize the binding hot spots in the interactions of the PA-PB1 complex, an 8 ns molecular dynamics simulation of the subunit PA-PB1 combined with MM-PBSA (molecular mechanics Poisson-Boltzmann surface area), MM-GBSA (molecular mechanics generalized Born surface area) computations and virtual alanine scanning were performed. The results from the free energy decomposition indicate that the intermolecular van der Waals interaction and the nonpolar solvation term provide the driving force for binding process. Through the pair interaction analysis and virtual alanine scanning, we identified the binding hot spots of PA and the basic binding motif of PB1. This information can provide some insights for the structure-based RNA-dependent RNA polymerase inhibitors design. The identified binding motif can be used as the starting point for the rational design of small molecules or peptide mimics. This study will also lead to new opportunities toward the development of new generation therapeutic agents exhibiting specificity and low resistance to influenza virus.