title: DNA aptamers to human immunodeficiency virus reverse transcriptase selected by a primer-free SELEX method: characterization and comparison with other aptamers.
abstract: A 30-nucleotide DNA aptamer (5'-AGGAAGGCTTTAGGTCTGAGATCTCGGAAT-3', denoted PF1) selected for high affinity to human immunodeficiency virus reverse transcriptase (HIV RT) using a primer-free SELEX (systematic evolution of ligands by exponential enrichment) method was characterized to determine features promoting tight binding. PF1's equilibrium dissociation constant for RT was ∼80 nM, over 10-fold lower than a random 30-mer. Changing the 2 terminal diguanosine repeats (underlined above) to diadenosine or dithymidine modestly decreased binding. Any changes to the 2 central diguanosines dramatically decreased binding. Binding was highly sensitive to length, with any truncations that deleted part of the 4 diguanosine motifs resulting in a 6-fold or more decrease in affinity. Even a construct with all the diguanosine motifs but lacking the 5' terminal A and 3 nucleotides at the 3' end showed ∼3-fold binding decrease. Changes to the nucleotides between the diguanosines, even those that did not alter PF1's low secondary structure (free energy of folding ΔG=-0.61 kcal/mol), dramatically decreased binding, suggesting sequence specificity. Despite the diguanosine motifs, circular dichroism (CD) spectra indicated that PF1 did not form a G-quartet. PF1 inhibited HIV RT synthesis with a half-maximal inhibitory value (IC(50)) of ∼60 nM. Larger, more structured RT DNA aptamers based on the HIV polypurine tract and those that formed G-quartets (denoted S4 and R1T) were more potent inhibitors, with IC(50) values of ∼4 and ∼1 nM, respectively. An RNA pseudoknot aptamer (denoted 1.1) showed an IC(50) near 4 nM. Competition binding assays with PF1 and several previously characterized RT aptamers indicated that they all bound at or near the primer-template pocket. These other more structured and typically larger aptamers bound more tightly than PF1 to RT based on filter binding assays. Results indicate that PF1 represents a new class of RT aptamers that are relatively small and have very low secondary structure, attributes that could be advantageous for further development as HIV inhibitors.
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland College Park, College Park, Maryland 20742, USA.
authors.forename: Yi-Tak
authors.initials: YT
authors.lastname: Lai
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: DeStefano
mesh_terms: D052157:Aptamers, Nucleotide; D001483:Base Sequence; D002942:Circular Dichroism; D054856:G-Quadruplexes; D054303:HIV Reverse Transcriptase / Q000235:genetics*; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology; D052156:SELEX Aptamer Technique; D013816:Thermodynamics
chemical_list: D052157:Aptamers, Nucleotide; D018894:Reverse Transcriptase Inhibitors; C514824:reverse transcriptase, Human immunodeficiency virus 1; D054303:HIV Reverse Transcriptase