Effect of P-chirality of internucleotide bonds on B-Z conversion of stereodefined self-complementary phosphorothioate oligonucleotides of the [PS]-d(CG)4 and [PS]-d(GC)4 series.
Diastereomerically pure, partially modified (in selected positions) or fully modified phosphorothioate oligomers of the [PS]-d(CG)(4) and [PS]-d(GC)(4) series were investigated with respect to their ability to adopt the left-handed conformation at high sodium chloride concentration. NaCl induces the B-Z transition of [All-S(P)R(P)-PS]-d(CG)(4) with a midpoint of transition at ca. 2 M, which is approximately 1 M less than for unmodified d(CG)(4). Also, [All-R(P)S(P)-PS]-d(GC)(4) at 5 M NaCl converts to the Z form to the extent of ca. 55%, while the unmodified d(GC)(4) counterpart does not convert at all. This enhanced ability of stereodefined phosphorothioate oligomers to adopt the Z conformation is discussed in terms of already known structural factors (hydrogen bonding and water bridges) facilitating the B-Z transition, identified for unmodified d(CG)(n) oligonucleotides. By CD spectroscopy, the [All-S(P)-PS]-d(CG)(4) oligomer at a NaCl concentration higher than 0.01 M adopts a unique conformation as assessed from the presence of an additional negative band centered at 282 nm.
Boczkowska
M
M
Department of Bioorganic Chemistry, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 L-ódz, Poland. mboczkow@bio.cbmm.lodz.pl
Guga
P
P
Karwowski
B
B
Maciaszek
A
A
D001482:Base Composition; D001483:Base Sequence; D002678:Chimera; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D003849:Deoxyguanosine / Q000737:chemistry; D015226:Dinucleoside Phosphates / Q000737:chemistry*; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013237:Stereoisomerism; D013816:Thermodynamics; D013873:Thionucleotides / Q000737:chemistry*
D015226:Dinucleoside Phosphates; D009838:Oligodeoxyribonucleotides; D013873:Thionucleotides; C054544:2'-deoxyguanylyl-(3'-5')-2'-deoxycytidine; D012965:Sodium Chloride; C041754:tetra(deoxycytidylic acid-deoxyguanylic acid); D004247:DNA; D003849:Deoxyguanosine