title: Unexpected A-form formation of 4'-thioDNA in solution, revealed by NMR, and the implications as to the mechanism of nuclease resistance.
abstract: Fully modified 4'-thioDNA, an oligonucleotide only comprising 2'-deoxy-4'-thionucleosides, exhibited resistance to an endonuclease, in addition to preferable hybridization with RNA. Therefore, 4'-thioDNA is promising for application as a functional oligonucleotide. Fully modified 4'-thioDNA was found to behave like an RNA molecule, but no details of its structure beyond the results of circular dichroism analysis are available. Here, we have determined the structure of fully modified 4'-thioDNA with the sequence of d(CGCGAATTCGCG) by NMR. Most sugars take on the C3'-endo conformation. The major groove is narrow and deep, while the minor groove is wide and shallow. Thus, fully modified 4'-thioDNA takes on the A-form characteristic of RNA, both locally and globally. The only structure reported for 4'-thioDNA showed that partially modified 4'-thioDNA that contained some 2'-deoxy-4'-thionucleosides took on the B-form in the crystalline form. We have determined the structure of 4'-thioDNA in solution for the first time, and demonstrated unexpected differences between the two structures. The origin of the formation of the A-form is discussed. The remarkable biochemical properties reported for fully modified 4'-thioDNA, including nuclease-resistance, are rationalized in the light of the elucidated structure.
authors.affiliation: Supramolecular Biology, International Graduate School of Arts and Sciences, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan.
authors.forename: Akimasa
authors.initials: A
authors.lastname: Matsugami
authors.forename: Takako
authors.initials: T
authors.lastname: Ohyama
authors.forename: Masashi
authors.initials: M
authors.lastname: Inada
authors.forename: Naonori
authors.initials: N
authors.lastname: Inoue
authors.forename: Noriaki
authors.initials: N
authors.lastname: Minakawa
authors.forename: Akira
authors.initials: A
authors.lastname: Matsuda
authors.forename: Masato
authors.initials: M
authors.lastname: Katahira
mesh_terms: D002236:Carbohydrate Conformation; D004247:DNA / Q000737:chemistry; D044704:DNA, A-Form / Q000737:chemistry* / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000378:metabolism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D012996:Solutions; D013873:Thionucleotides / Q000737:chemistry* / Q000378:metabolism
chemical_list: D044704:DNA, A-Form; D012996:Solutions; D013873:Thionucleotides; D004247:DNA; D004706:Endodeoxyribonucleases