Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
Nucleic Acid Interaction Kinetics Modulate the Chaperone Activity of Retroviral Nucleocapsid Proteins
Retroviral nucleocapsid (NC) proteins are essential for several viral replication processes including specific genomic RNA packaging and reverse transcription. The nucleic acid chaperone activity of NC facilitates the latter process. In this study, we use bulk and single molecule methods to quantify the chaperone activity of NC proteins from human immunodeficiency virus type 1 (HIV-1), Moloney murine leukemia virus, Rous sarcoma virus, and human T-cell leukemia virus type one (HTLV-1). We find that the nucleic acid interaction properties of these proteins vary significantly depending on the virus, with HIV-1 NC showing rapid protein binding kinetics, significant duplex destabilization, and strong DNA aggregation, all properties that are believed to be critical components of nucleic acid chaperone activity. In contrast, HTLV-1 NC exhibits significant destabilization activity but extremely slow DNA interaction kinetics and poor aggregating capability. This result explains why HTLV-1 NC is a poor nucleic acid chaperone. However, removal of HTLV-1 NC?s anionic C-terminal domain (CTD) results in a protein with chaperone activity comparable to that of other retroviral NCs. Removal of the CTD also dramatically increases the protein-DNA interaction kinetics. These results suggest that HTLV-1 NC?s anionic CTD interacts with its cationic N-terminal domain (NTD), either intra- or intermolecularly, which in turn slows down the protein?s nucleic acid binding kinetics. This electrostatic attraction between bound molecules leads to polymerization of HTLV-1 NC on the nucleic acid, which inhibits nucleic acid aggregation, as well as rapid protein dissociation from single-stranded DNA. These results may also help to explain the mechanism by which the CTD of HTLV-1 NC prevents packaging of human APOBEC3G. This work was funded in part by Federal Funds from NCI, NIH under contract N01-CO-12400 (RJG).