title: Impact of sugar pucker on base pair and mispair stability.
abstract: The selection of nucleoside triphosphates by a polymerase is controlled by several energetic and structural features, including base pairing geometry as well as sugar structure and conformation. Whereas base pairing has been considered exhaustively, substantially less is known about the role of sugar modifications for both nucleotide incorporation and primer extension. In this study, we synthesized oligonucleotides containing 2'-fluoro-modified nucleosides with constrained sugar pucker in an internucleotide position and, for the first time, at a primer 3'-end. The thermodynamic stability of these duplexes was examined. The nucleoside 2'-deoxy-2'-fluoroarabinofuranosyluracil [U(2'F(ara))] favors the 2'-endo conformation (DNA-like), while 2'-deoxy-2'-fluororibofuranosyluracil [U(2'F(ribo))] favors the 3'-endo conformation (RNA-like). Oligonucleotides containing U(2'F(ara)) have slightly higher melting temperatures (T(m)) than those containing U(2'F(ribo)) when located in internucleotide positions or at the 3'-end and when correctly paired with adenine or mispaired with guanine. However, both modifications decrease the magnitude of DeltaH degrees and DeltaS degrees for duplex formation in all sequence contexts. In examining the thermodynamic properties for this set of oligonucleotides, we find entropy-enthalpy compensation is apparent. Our thermodynamic findings led to a series of experiments with DNA ligase that reveal, contrary to expectation based upon observed T(m) values, that the duplex containing the U(2'F(ribo)) analogue is more easily ligated. The 2'-fluoro-2'-deoxynucleosides examined here are valuable probes of the impact of sugar constraint and are also members of an important class of antitumor and antiviral agents. The data reported here may facilitate an understanding of the biological properties of these agents, as well as the contribution of sugar conformation to replication fidelity.
authors.affiliation: Department of Basic Sciences, School of Medicine, Loma Linda University, Loma Linda, California 92350, USA.
authors.forename: Adides A
authors.initials: AA
authors.lastname: Williams
authors.forename: Agus
authors.initials: A
authors.lastname: Darwanto
authors.forename: Jacob A
authors.initials: JA
authors.lastname: Theruvathu
authors.forename: Artur
authors.initials: A
authors.lastname: Burdzy
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Neidigh
authors.forename: Lawrence C
authors.initials: LC
authors.lastname: Sowers
mesh_terms: D020137:Base Pair Mismatch; D020029:Base Pairing; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000737:chemistry*; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000737:chemistry; D003857:Deoxyuridine / Q000031:analogs & derivatives / Q000737:chemistry; D029968:Escherichia coli Proteins / Q000737:chemistry; D006801:Humans; D008969:Molecular Sequence Data; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry; D009841:Oligonucleotides / Q000138:chemical synthesis; D000075223:Poly-ADP-Ribose Binding Proteins; D013816:Thermodynamics; D029867:Xenopus Proteins
chemical_list: D002241:Carbohydrates; D029968:Escherichia coli Proteins; D009692:Nucleic Acid Heteroduplexes; D009841:Oligonucleotides; D000075223:Poly-ADP-Ribose Binding Proteins; D029867:Xenopus Proteins; D011088:DNA Ligases; D000072481:DNA Ligase ATP; C000618816:DNA ligase III alpha protein, Xenopus; D003857:Deoxyuridine