Mutational analysis and allosteric effects in the HIV-1 capsid protein carboxyl-terminal dimerization domain.

The carboxyl-terminal domain (CTD, residues 146-231) of the HIV-1 capsid (CA) protein plays an important role in the CA-CA dimerization and viral assembly of the human immunodeficiency virus type 1. Disrupting the native conformation of the CA is essential for blocking viral capsid formation and viral replication. Thus, it is important to identify the exact nature of the structural changes and driving forces of the CTD dimerization that take place in mutant forms. Here, we compare the structural stability, conformational dynamics, and association force of the CTD dimers for both wild-type and mutated sequences using all-atom explicit-solvent molecular dynamics (MD). The simulations show that Q155N and E159D at the major homology region (MHR) and W184A and M185A at the helix 2 region are energetically less favorable than the wild-type, imposing profound negative effects on intermolecular CA-CA dimerization. Detailed structural analysis shows that three mutants (Q155N, E159D, and W184A) display much more flexible local structures and weaker CA-CA association than the wildtype, primarily due to the loss of interactions (hydrogen bonds, side chain hydrophobic contacts, and pi-stacking) with their neighboring residues. Most interestingly, the MHR that is far from the interacting dimeric interface is more sensitive to the mutations than the helix 2 region that is located at the CA-CA dimeric interface, indicating that structural changes in the distinct motif of the CA could similarly allosterically prevent the CA capsid formation. In addition, the structural and free energy comparison of the five residues shorter CA (151-231) dimer with the CA (146-231) dimer further indicates that hydrophobic interactions, side chain packing, and hydrogen bonds are the major, dominant driving forces in stabilizing the CA interface.