A PROTON-COUPLED CONFORMATIONAL SWITCH OF ESCHERICHIA-COLI 5S RIBOSOMAL-RNA
A PROTON-COUPLED CONFORMATIONAL SWITCH OF ESCHERICHIA-COLI 5S RIBOSOMAL-RNA
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DOI：
10.1073/pnas.77.6.3360
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发表时间：
1980-01-01
期刊：
影响因子：
--
通讯作者：
CROTHERS, DM
中科院分区：
文献类型：
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作者：
KAO, TH;CROTHERS, DM
报道了大肠杆菌5S rRNA早期熔融转变的温度跳跃动力学研究。在266 nm处发现了一个与浓度无关的单一可测量的弛豫时间。该过程的转变温度tm(在0-40℃的范围内)。C)监测作为镁离子、钠离子、钾离子、亚精胺和氢离子浓度的函数。与通常盐对核酸稳定性的影响相反，单价和多价反离子的加入降低了早期熔融转变的tm。在7-8的生理范围内，tm对pH有很强的依赖性。数据的定量分析表明，当有序(低温)形式熔化时，大约有0.7个质子被释放，而大约2Na+(或K+)和0.5Mg2+被熔融(高温)形式吸收。测得该转变的热焓为15-20kcal/mol(63-84kJ/mol)，给出了转变的正反向速率常数和活化能，以及离子对转变动力学的影响。扩散常数测量表明，低温形式的摩擦系数比高温形式的摩擦系数大10%左右。这些数据表明，一种能够结合质子的低温三级结构。PH、温度或反离子浓度的增加(都处于接近生理的值)会导致三级构象转换到更紧密的形式，具有更多的反离子结合但较少的质子结合。文中还讨论了这种转变可能的生理作用。
Temperature-jump kinetic studies of the early melting transition of E. coli 5S rRNA are reported. A single measurable relaxation time .tau., independent of concentration, was found at 266 nm. The transition temperature tm for this process (in the range from 0-40.degree. C) as a function of Mg2+, Na+, K+, spermidine and H+ concentrations was monitored. Contrary to the usual effect of salts on nucleic acid stability, addition of mono- and multivalent counterions decreases tm for the early melting transition. A strong dependence of tm on pH in the physiological range of 7-8 was found. Quantitative analysis of the data indicates that about 0.7 protons are released when the ordered (low-temperature) form melts, whereas about 2 Na+ (or K+) and 0.5 Mg2+ are taken up by the melted (high-temperature) form. The enthalpy of the transition was estimated to be 15-20 kcal/mol (63-84 kJ/mol); the forward and reverse rate constant and activation energies for the transition, along with the influence of ions on the transition dynamics are reported. Diffusion constant measurements reveal that the low-temperature form has a frictional coefficient about 10% larger than that of the high-temperature form. The data imply a low-temperature tertiary structure capable of binding a proton. Increase of pH, temperature or counterion concentration (all at near-physiological values) causes a tertiary conformational switch to a more compact form that has greater counterion binding but less proton binding. Possible physiological roles for the transition are discussed.