ON THE STABILITY OF NUCLEIC-ACID STRUCTURES IN SOLUTION - ENTHALPY ENTROPY COMPENSATIONS, INTERNAL ROTATIONS AND REVERSIBILITY
ON THE STABILITY OF NUCLEIC-ACID STRUCTURES IN SOLUTION - ENTHALPY ENTROPY COMPENSATIONS, INTERNAL ROTATIONS AND REVERSIBILITY
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DOI：
10.1093/nar/21.9.2051
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发表时间：
1993-05-11
影响因子：
14.9
通讯作者：
WILLIAMS, DH
中科院分区：
文献类型：
--
作者：
SEARLE, MS;WILLIAMS, DH
自由碱基和核苷酸的自缔合（堆叠）、二核苷酸中的分子内堆叠、双链DNA和RNA中的最近邻碱基对堆叠相互作用以及发夹环的形成的热力学说明了焓/熵补偿。大的堆叠有序性与大的负熵变化相关联，这确保DELTAG很小，允许容易可逆的关联 在 溶液 我们 合理化焓/熵补偿，参考剩余运动和扭转振动，当-Δ H几乎等于kT（室温下的热能）时，比当-Δ H> > kT时，剩余运动和扭转振动对结合做出更大的熵贡献。我们提出了一个因式分解的实验自由能螺旋形成的近似贡献，从限制旋转，疏水相互作用，静电相互作用，由于基地堆叠，和贡献氢键，并估算每个转子的不利自由能成本（主要是熵）的磷酸骨架排序为1.9和5.4 kJ mol-1之间[平均超过12转子每碱基对的A-U上的A-U堆叠（下限）和C-G堆叠上的G-C（上限）]。最大的成本与最放热的堆积相互作用有关，而值的范围与烃链融合数据的早期结论（较低的值）一致，并且与涉及严重限制的小分子共价异构化的熵变化（较高的值）一致。
The thermodynamics of self-association (stacking) of free bases and nucleotides, intramolecular stacking in dinucleotides, nearest-neighbour base pair stacking interactions in duplex DNA and RNA, and the formation of hairpin loops illustrate enthalpy/entropy compensations. Large stacking exothermicities are associated with large negative entropy changes that ensure that DELTAG is small, permitting readily reversible associations in solution. We rationalise enthalpy/entropy compensations with reference to residual motions and torsional vibrations which make a larger entropic contribution to binding when - DELTAH almost-equal-to kT (thermal energy at room temperature), than when - DELTAH > > kT. We present a factorisation of experimental free energies for helix formation in terms of approximate contributions from the restriction of rotations, hydrophobic interactions, electrostatic interactions due to base stacking, and contributions from hydrogen bonding, and estimate the adverse free energy cost per rotor (mainly entropy) of ordering the phosphate backbone as between 1.9 and 5.4 kJ mol-1 [averaged over 12 rotors per base pair for A-U on A-U stacking (lower limit), and G-C on C-G stacking (upper limit)]. The largest cost is associated with the most exothermic stacking interactions, while the range of values is consistent with earlier conclusions from data on the fusion of hydrocarbon chains (lower value), and with entropy changes in covalent isomerisations of small molecules involving severe restrictions (upper value).