title: The structures and relative stabilities of d(G x G) reverse Hoogsteen, d(G x T) reverse wobble, and d(G x C) reverse Watson-Crick base-pairs in DNA crystals.
abstract: We have solved the structures of the homoduplex d(Gm5CGCGCG)2, and the heteroduplexes d(GCGCGCG)/d(TCGCGCG) and d(GCGCGCG)/d(CCGCGCG). The structures form six base-pairs of identical Z-DNA duplexes with single nucleotides overhanging at the 5'-ends. The overhanging nucleotide from one strand remains stacked and sandwiched between the blunt-ends of two adjacent Z-DNA duplexes, while the overhanging base of the opposing strand is extra-helical. The stacked and the extra-helical bases from adjacent duplexes pair to form a distorted d(G x G) reverse Hoogsteen base-pair in the d(Gm5CGCGCG)2 homoduplex, and d(G x T) reverse wobble and d(G x C) reverse Watson-Crick base-pairs in the d(GCGCGCG)/d(TCGCGCG) and d(GCGCGCG)/d(CCGCGCG) heteroduplexes, respectively. Interestingly, only the d(G,T) and d(G x C) base-pairs were observed in the heteroduplexes, suggesting that both the d(G x T) reverse wobble and d(G x C) reverse Watson-Crick base-pairs are more stable in this crystal environment than the d(G x G) reverse Hoogsteen base-pair. To estimate the relative stability of the three types of reverse base-pairs, crystals were grown using various mixtures of sequences and their strand compositions analyzed by mass spectrometry. The d(G x C) reverse Watson-Crick base-pair was estimated to be more stable by approximately 1.5 kcal/mol and the d(G x T) reverse wobble base-pair more stable by approximately 0.5 kcal/mol than the d(G x G) reverse Hoogsteen base-pair. The step during crystallization responsible for discriminating between the strands in the crystal is highly cooperative, suggesting that it occurs during the initial nucleating event of crystal growth.
authors.affiliation: Department of Biochemistry and Biophysics, Oregon State University, Corvallis 97331, USA.
authors.forename: B H
authors.initials: BH
authors.lastname: Mooers
authors.forename: B F
authors.initials: BF
authors.lastname: Eichman
authors.forename: P S
authors.initials: PS
authors.lastname: Ho
mesh_terms: D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry*; D003841:Deoxycytidine / Q000737:chemistry; D003849:Deoxyguanosine / Q000737:chemistry; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D013936:Thymidine / Q000737:chemistry
chemical_list: D009838:Oligodeoxyribonucleotides; D003841:Deoxycytidine; D004247:DNA; D003849:Deoxyguanosine; D013936:Thymidine