Molecular determinants of HIV-1 NCp7 chaperone activity in maturation of the HIV-1 dimerization initiation site

Human immunodeficiency virus genome dimerization is initiated through an RNA–RNA kissing interaction formed via the dimerization initiation site (DIS) loop sequence, which has been proposed to be converted to a more thermodynamically stable linkage by the viral p7 form of the nucleocapsid protein (NC). Here, we systematically probed the role of specific amino acids of NCp7 in its chaperone activity in the DIS conversion using 2-aminopurine (2-AP) fluorescence and nuclear magnetic resonance spectroscopy. Through comparative analysis of NCp7 mutants, the presence of positively charged residues in the N-terminus was found to be essential for both helix destabilization and strand transfer functions. It was also observed that the presence and type of the Zn finger is important for NCp7 chaperone activity, but not the order of the Zn fingers. Swapping single aromatic residues between Zn fingers had a significant effect on NCp7 activity; however, these mutants did not exhibit the same activity as mutants in which the order of the Zn fingers was changed, indicating a functional role for other flanking residues. RNA chaperone activity is further correlated with NCp7 structure and interaction with RNA through comparative analysis of nuclear magnetic resonance spectra of NCp7 variants, and complexes of these proteins with the DIS dimer.