Solution structures of the i-motif tetramers of D(TCC), D(5MCCT) and D(T5MCC). Novel NOE connections between amino protons and sugar protons
SOME OF THE CYTIDINES ARE PROTONATED AT THE N3 POSITION. THESE RESIDUES HAVE BEEN ASSIGNED THE RESIDUE NAME C IN THE ENTRY AND ATOM H3 HAS BEEN FOOTNOTED.
Solution structures of the i-motif tetramers of d(TCC), d(5methylCCT) and d(T5methylCC): novel NOE connections between amino protons and sugar protons.
5MC STANDS FOR 5-METHYLCYTIDINE. THE STRUCTURE IS FORMED OF FOUR EQUIVALENT 5MCCT STRANDS DESIGNATED A, B, C, D. STRANDS A AND C, CONNECTED BY TWO HEMI-PROTONATED BASE PAIRS (5MC1.5MC1+ AND C2.C2+), FORM A PARALLEL-STRANDED DUPLEX. THE RELATION BETWEEN STRANDS B AND D IS THE SAME AS THAT BETWEEN STRANDS A AND C. THE STRANDS OF EACH DUPLEX ARE RELATED BY A LONGITUDINAL TWO-FOLD SYMMETRY AXIS. THE DUPLEXES HAVE THE SAME LONGITUDINAL AXIS, AND THEY ARE ANTI-PARALLEL. THEIR HEMI-PROTONATED C.C+ BASE PAIRS ARE INTERCALATED FACE-TO-FACE. THE DUPLEXES CAN BE TRANSFORMED INTO ONE ANOTHER BY A 180 DEGREE ROTATION AROUND A TWO-FOLD AXIS PERPENDICULAR TO THE LONGITUDINAL AXIS, AND CONSEQUENTLY AROUND A THIRD AXIS PERPENDICULAR TO THE FIRST TWO. THE H3 IMINO PROTONS OF THE HEMI-PROTONATED 5MC1.5MC1+ PAIRS WERE NOT INCORPORATED IN THE COMPUTATIONS. THOSE OF THE C2.C2+ PAIRS WERE ARBITRARILY LOCATED ON THE C2 RESIDUES OF STRANDS A AND B, RESPECTIVELY.