Positive heat capacity change upon specific binding of translation initiation factor eIF4E to mRNA 5′ cap
Positive heat capacity change upon specific binding of translation initiation factor eIF4E to mRNA 5′ cap
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DOI：
10.1021/bi0258142
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发表时间：
2002-10-08
期刊：
影响因子：
2.9
通讯作者：
Stolarski, R
中科院分区：
文献类型：
--
作者：
Niedzwiecka, A;Stepinski, J;Stolarski, R
真核生物起始因子eIF 4 E对mRNA 5'端帽的特异性识别是翻译起始的限速步骤。荧光光谱法和高灵敏度等温滴定量热法被用来研究eIF 4 E结合到一个帽类似物，7-甲基GpppG的热力学。van 't霍夫图显示了非线性，其特征在于意外的大的正摩尔热容变化（Δ C（p）度= +1.92 +/-0.93 kJ.mol（-1）.K-1），这通过直接ITC测量（Δ C（p）度Δ C（p）度= +1.941 +/-0.059 kJ.mol（-1）.K-1）得到了证实。这种独特的结果似乎来自于结合位点内结合和电荷相关相互作用后的广泛额外水合作用。作为正DeltaC（p）度的结果，热力学驱动力的性质随着温度的升高而改变，从焓驱动和熵相反，通过生物温度范围内的焓和熵驱动，变成熵驱动和熵相反。van 't霍夫和量热焓值的比较提供了结合时N（1）处配体质子化的证据，这是帽-eIF 4 E复合物的紧密稳定所需的。分析了二核苷酸帽类似物的分子内自堆积，以揭示这种偶联过程对eIF 4 E-mRNA 5'帽相互作用的热力学参数的影响。7-甲基GpppG构象的温度依赖性变化显著地将结合的固有Δ H（0）度= -72.9 +/-4.2 kJ·mol（-1）和Δ S（0）度= -116 +/-58 J.mol（-1）·K-1移动到较小的负结果值，通过Δ H（sst）度= +9.76 +/- 1.15 kJ·mol（-1）和Δ S（sst）度= +24.8 +/- 2.1 J·mol（-1）·K-1（在293 K下），而相应的Δ C（psst）度-0.0743 +/-0.0083 kJ·mol（-1）·K-1与总Δ C（p）度相比可以忽略不计。
Specific recognition of the mRNA 5' cap by eukaryotic initiation factor eIF4E is a rate-limiting step in the translation initiation. Fluorescence spectroscopy and high-sensitivity isothermal titration calorimetry were used to examine the thermodynamics of eIF4E binding to a cap-analogue, 7-methylGpppG. A van't Hoff plot revealed nonlinearity characterized by an unexpected, large positive molar heat capacity change (DeltaC(p)degrees = +1.92 +/- 0.93 kJ.mol(-1).K-1), which was confirmed by direct ITC measurements (DeltaC(p)degrees DeltaC(p)degrees = +1.941 +/- 0.059 kJ.mol(-1).K-1). This unique result appears to come from an extensive additional hydration upon binding and charge-related interactions within the binding site. As a consequence of the positive DeltaC(p)degrees, the nature of the thermodynamic driving force changes with increasing temperature, from enthalpy-driven and entropy-opposed, through enthalpy- and entropy-driven in the range of biological temperatures, into entropy-driven and enthalpy-opposed. Comparison of the van't Hoff and calorimetric enthalpy values provided proof for the ligand protonation at N(1) upon binding, which is required for tight stabilization of the cap-eIF4E complex. Intramolecular self-stacking of the dinucleotide cap-analogue was analyzed to reveal the influence of this coupled process on the thermodynamic parameters of the eIF4E-mRNA 5' cap interaction. The temperature-dependent change in the conformation of 7-methylGpppG shifts significantly the intrinsic DeltaH(0)degrees = -72.9 +/- 4.2 kJ.mol(-1) and DeltaS(0)degrees = -116 +/- 58 J.mol(-1).K-1 of binding to the less negative resultant values, by DeltaH(sst)degrees = +9.76 +/- 1.15 kJ.mol(-1) and DeltaS(sst)degrees = +24.8 +/- 2.1 J.mol(-1).K-1 (at 293 K), while the corresponding DeltaC(psst)degrees -0.0743 +/- 0.0083 kJ.mol(-1).K-1 is negligible in comparison with the total DeltaC(p)degrees.