TAR-RNA Recognition by a Novel Cyclic Aminoglycoside Analogue

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The formation of the Tat-protein/TAR RNA complex is a crucial step in the regulation of Human Immunodeficiency Virus (HIV)-gene expression. To obtain fulllength viral transcripts the Tat/TAR complex has to recruit the positive transcription elongation factor complex (P-EFTb), which interacts with TAR through its CyclinT1 (CycT1) component. Mutational studies identified the TAR hexanucleotide loop as a crucial region for contacting CyclinT1. Interfering with the interaction between the Tat/CycT1 complex and the TAR RNA is an attractive strategy for the design of anti- HIV drugs. Positively charged molecules, like aminoglycosides or peptidomimetics, bind the TAR RNA, disrupting the Tat/TAR complex. Here, we investigate the complex between the HIV-2 TAR RNA and a neooligoaminodeoxysaccharide by NMR spectroscopy. In contrast to other aminoglycosides, this novel aminoglycoside analogue contacts simultaneously the bulge residues required for Tat binding and the A35 residue of the hexanucleotide loop. Upon complex formation, the loop region undergoes profound conformational changes. The novel binding mode, together with the easy accessibility of derivatives for the neooligoaminodeoxysaccharide, could open the way to the design of a new class of TAR RNA binders, which simultaneously inhibit the formation of both the Tat/TAR binary complex and the Tat/TAR/CyclinT1 ternary complex by obstructing both the bulge and loop regions of the RNA.