Mooren M M, Pulleyblank D E, Wijmenga S S, van de Ven F J, Hilbers C W
NSR Centre for Molecular Structure, Design, and Synthesis, Laboratory of Biophysical Chemistry, University of Nijmegen, The Netherlands.
Biochemistry. 1994 Jun 14;33(23):7315-25. doi: 10.1021/bi00189a037.
The 15-residue oligonucleotide d(TCTCTC-TTT-GAGAGA) forms a hairpin structure with a loop of three thymidine residues at neutral pH or above. The three-dimensional solution structure of this oligonucleotide has been determined by means of two-dimensional nuclear magnetic resonance methods. Interproton distance constraints derived from NOEs, in combination with torsion angle constraints obtained from J-coupling constants were used in the variable target function program DIANA to derive the hairpin structure. It was found that hairpins with two different loop conformations fit the NMR data, i.e. an equilibrium between these two conformational states can only fully explain the NOE data available. In one state, loop residue T7 is turned into the minor groove, while in the second state residue T8 is in the minor groove. In both conformations the phosphate backbone changes its direction by 180 degrees between residues T9 and G10. Concomitantly, torsion angles zeta of T9 and alpha of G10 both adopt a gauche(+) conformation and gamma of residue G10 adopts a trans conformation to induce this complete change in the direction of the backbone.
15个残基的寡核苷酸d(TCTCTC-TTT-GAGAGA)在中性pH或更高pH条件下形成一种发夹结构，其环由三个胸腺嘧啶残基组成。该寡核苷酸的三维溶液结构已通过二维核磁共振方法确定。从核Overhauser效应(NOEs)得出的质子间距离约束，与从J耦合常数获得的扭转角约束相结合，用于可变目标函数程序DIANA中以推导出发夹结构。结果发现，具有两种不同环构象的发夹符合核磁共振数据，即这两种构象状态之间的平衡才能完全解释现有的NOE数据。在一种状态下，环残基T7转向小沟，而在第二种状态下残基T8位于小沟中。在两种构象中，磷酸主链在残基T9和G10之间改变其方向180度。同时，T9的ζ扭转角和G10的α扭转角均采用顺式(+)构象，而残基G10的γ扭转角采用反式构象，以诱导主链方向的这种完全变化。
