LAUSR

Integrases participates in two important steps for virus replication such as 3'-end processing of viral DNA ( vDNA) and nuclear entry of host DNA ( hDNA). In this work insight into the structural changes in intasome of prototype foamy virus integrase (PFV-IN) complexed with vDNA from classical molecular dynamic (MD) simulations are done. Analysis of the results reveal the existence of alternative conformations of the enzyme active site indicating that 3'-end processing reaction can occur according to three different pathways, and taking place with the possible participation of aspartate 185, of a neighbouring phosphate group, or involving internal phosphate group of the substrate. In this work one of them, the so-called 'substrate-assisted' mechanism was explored, by QM/MM methods. The free energy barriers of 34.4 kcal∙mol-1 for the first and 35.3 kcal∙mol-1 for the second step of reaction computed with free energy perturbation (FEP) methods at M06-2X/AMBER level, show that 3'-end processing has to proceed via a different mechanism than studied herein. Nevertheless, the obtained results are in good agreement with the experimental observations, that the substitution of the key atom for this mechanism, oxygen by sulphur, did not influence the catalysis. Additionally, the obtained mechanism reveals significant similarities to the previously studied 'substrate-assisted' mechanism in twister ribozyme. The possible role of Mg2+ in the active site is discussed.