Specificity of neomycin analogues bound to the packaging region of human immunodeficiency virus type 1 RNA.

The packaging region of HIV-1 RNA contains a number of structural features which are important in the life cycle of the virus, making this segment of RNA a potential target for new types of AIDS-directed drugs. We studied the binding of three neomycin analogues (neo-guanidino, neo-acridine, and neo-neo) to a 171-mer RNA molecule from the packaging region of HIV-1 using quantitative footprinting and circular dichroism. Neo-guanidino produced footprinting patterns and effects on the CD similar to those observed for neomycin and paromomycin, indicating that all three compounds bind to the same regions of the 171-mer. Neo-guanidino binds to SL 1 where it joins the large internal loop, near a bulge in the stem of SL 1, and on SL 2. Neo-acridine, which has an acridine attached to neomycin, and neo-neo, which has two neomycins linked by a flexible tether, bind bivalently, and give very different footprinting and CD results from the other compounds. The neomycin portion of neo-acridine binds to the same sites as neomycin, while the attached acridine group appears to bind to a duplex region in the main stem of the folded 171-mer. Since the footprinting data for this analogue show few enhancements, bivalent binding of neo-acridine appears to stabilize the folded structure of RNA by effectively 'stapling' parts of the structure together. Neo-neo induces significant structural changes in RNA where neomycin binds. This may be related to the inability of both neomycins of neo-neo it find optimal binding sites adjacent to one another without changing RNA structure. The intensity of a strong negative CD band in the spectrum of psi-RNA at 208 nm is sensitive to drug-induced changes in RNA structure. Neo-guanidino and neo-neo (also neomycin and paromomycin), which change RNA structure, cause an increase in intensity while neo-acridine, which induces little distortion to RNA, causes a decrease in intensity. Molecular modeling analysis shows that C-5' of ribose of neo-acridine and neo-neo must be directed away from the binding pocket when these analogues are bivalently bound to RNA. This study showed how variations in the structure of aminoglycosides lead to different binding specificity to part of the packaging region of HIV-1. Such knowledge will be important in design of drugs to target this region.