Abstract
BackgroundThe nucleocapsid domain of Gag and mature nucleocapsid protein (NC) act as nucleic acid chaperones and facilitate folding of nucleic acids at critical steps of retroviral replication cycle. The basic N-terminus of HIV-1 NC protein was shown most important for the chaperone activity. The HIV-2 NC (NCp8) and HIV-1 NC (NCp7) proteins possess two highly conserved zinc fingers, flanked by basic residues. However, the NCp8 N-terminal domain is significantly shorter and contains less positively charged residues. This study characterizes previously unknown, nucleic acid chaperone activity of the HIV-2 NC protein.ResultsWe have comparatively investigated the in vitro nucleic acid chaperone properties of the HIV-2 and HIV-1 NC proteins. Using substrates derived from the HIV-1 and HIV-2 genomes, we determined the ability of both proteins to chaperone nucleic acid aggregation, annealing and strand exchange in duplex structures. Both NC proteins displayed comparable, high annealing activity of HIV-1 TAR DNA and its complementary nucleic acid. Interesting differences between the two NC proteins were discovered when longer HIV substrates, particularly those derived from the HIV-2 genome, were used in chaperone assays. In contrast to NCp7, NCp8 weakly facilitates annealing of HIV-2 TAR RNA to its complementary TAR (−) DNA. NCp8 is also unable to efficiently stimulate tRNALys3 annealing to its respective HIV-2 PBS motif. Using truncated NCp8 peptide, we demonstrated that despite the fact that the N-terminus of NCp8 differs from that of NCp7, this domain is essential for NCp8 activity.ConclusionOur data demonstrate that the HIV-2 NC protein displays reduced nucleic acid chaperone activity compared to that of HIV-1 NC. We found that NCp8 activity is limited by substrate length and stability to a greater degree than that of NCp7. This is especially interesting in light of the fact that the HIV-2 5′UTR is more structured than that of HIV-1. The reduced chaperone activity observed with NCp8 may influence the efficiency of reverse transcription and other key steps of the HIV-2 replication cycle.
Highlights
The nucleocapsid domain of Gag and mature nucleocapsid protein (NC) act as nucleic acid chaperones and facilitate folding of nucleic acids at critical steps of retroviral replication cycle
nucleic acid chaperone (NAC) activity of HIV-2 nucleocapsid protein (NCp8) and HIV-1 nucleocapsid protein (NCp7) in assays with Human immunodeficiency virus type 1 (HIV-1) Trans-activation response element (TAR) oligonucleotides was similar, but when longer HIV-1 substrates or those derived from the HIV-2 genome were used, interesting differences between these two proteins were discovered
NCp8 was unable to efficiently stimulate tRNALys3 annealing to its respective HIV-2 primer binding site (PBS) motif
Summary
The nucleocapsid domain of Gag and mature nucleocapsid protein (NC) act as nucleic acid chaperones and facilitate folding of nucleic acids at critical steps of retroviral replication cycle. HIV1 and HIV-2 share a similar genome organization, virion structure and replication cycle Like other retroviruses they possess a dimeric genome assembled from two identical RNA sense strands interacting near their 5′-ends. In broad specificity and facilitate their folding by destabilizing misfolded, kinetically trapped structures and enabling the formation of the thermodynamically most favored form [6,7,8,9]. They do not require ATP and their binding is no longer required once the most stable nucleic acid structure is reached [9,10]
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