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Base flexibility in HIV-2 TAR RNA mapped by solution (15)N, (13)C NMR relaxation
Kwaku T Dayie1, Alexander S Brodsky, James R Williamson
1Department of Molecular Biology and the Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Abstract:
Binding of the HIV tat protein to the TAR (transactivating response region) RNA element activates transcription of the HIV viral genome. The complex of TAR with argininamide serves as a model for the RNA conformation in the tat-TAR complex. The dynamics of the HIV-2 TAR-argininamide complex was investigated by measurements of the relaxation rates of protonated base carbon and nitrogen nuclei. Six auto-correlation rates as well as cross-correlation rates were measured to map the frequencies of base motion in the HIV-2 TAR-argininamide complex. These measurements reveal a broad range of dynamic heterogeneity exhibited by hexanucleotide loop, the dinucleotide bulge, and the A-form helical regions. U23 in the bulge undergoes the largest dynamic change on binding argininamide, while U25 remains flexible, reflecting the large conformational change that is triggered upon ligand binding.