The dynamics of interconverting D- and E-forms of the HIV-1 integrase N-terminal domain

The N-terminal domain (NTD) of HIV-1 integrase adopts two inter-converting forms (D- and E-) due to their specific coordination of a Zn²⁺ ion by an HHCC motif. Mutational studies on NTD have suggested the importance of conformational transition in regulating the functions of tetramers and dimers of HIV-1 integrase. This study explores the stability and dynamics of native NTD forms and the conformational transition between D- and E-forms using molecular dynamics simulations elucidating their role in regulation of viral and host DNA integration. Simulation of native forms of NTD revealed stable dynamics. Transition studies between D- and E-forms using conventional molecular dynamics simulations for 50 ns partially revealed conformational change towards the target during D- to -E simulation (the extension of α1-helix), which failed in the E- to -D simulation. This could be attributed to the existence of the D-form (?1,945.907 kCal/mol) in higher energy than the E-form (?2,002.383 kCal/mol). The conformational transition pathway between these two states was explored using targeted molecular dynamics simulations. Analysis of the targeted molecular dynamics trajectories revealed conformations closer to the experimentally-reported intermediate form of an NTD during the transition phase. The role of Met22 in stabilizing the E-form was studied by simulating the E-form with Met22Ala mutation, revealing a highly dynamic α1-helix as compared to the native form. The present study reveals the significant role of the Zn²⁺ ion-coordinated HHCC motif and its interaction with Met22 as the basis for understanding the biological implications of D- and E-forms of the NTD in regulating integration reaction.