Department of Biochemistry and Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996, United States.
Biochemistry. 2011 Nov 1;50(43):9309-17. doi: 10.1021/bi2011916. Epub 2011 Oct 10.
The results presented here show the first known observation of opposite signs of change in heat capacity (ΔC(p)) of two structurally similar ligands binding to the same protein site. Neomycin and paromomycin are aminoglycoside antibiotics that are substrates for the resistance-conferring enzyme, the aminoglycoside acetyltransferase-(3)-IIIb (AAC). These antibiotics are identical to one another except at the 6' position where neomycin has an amine and paromomycin has a hydroxyl. The opposite trends in ΔC(p) of binding of these two drugs to AAC suggest a differential exposure of nonpolar amino acid side chains. Nuclear magnetic resonance experiments further demonstrate significantly different changes in AAC upon interaction with neomycin and paromomycin. Experiments in H(2)O and D(2)O reveal the first observed temperature dependence of solvent and vibrational contributions to ΔC(p). Coenzyme A significantly influences these effects. Together, the data suggest that AAC exploits solvent properties to facilitate favorable thermodynamic selection of antibiotics.
这里呈现的结果首次观察到两种结构相似的配体结合到相同的蛋白质位点时，热容量 (ΔC(p)) 变化的符号相反。新霉素和巴龙霉素是氨基糖苷类抗生素，是具有抗性的酶——氨基糖苷乙酰转移酶-(3)-IIIb（AAC）的底物。这两种抗生素彼此完全相同，只是在 6'位置上，新霉素有一个胺基，而巴龙霉素有一个羟基。这两种药物与 AAC 结合的 ΔC(p) 呈相反趋势，表明非极性氨基酸侧链的暴露程度不同。核磁共振实验进一步证明了 AAC 在与新霉素和巴龙霉素相互作用时发生了显著不同的变化。在 H(2)O 和 D(2)O 中的实验揭示了溶剂和振动对 ΔC(p) 贡献的首次观察到的温度依赖性。辅酶 A 显著影响这些效应。综合数据表明，AAC 利用溶剂性质促进抗生素的有利热力学选择。
