A novel view of pH titration in biomolecules
A novel view of pH titration in biomolecules
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DOI：
10.1021/bi002740q
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发表时间：
2001-03-27
期刊：
影响因子：
2.9
通讯作者：
Ullmann, GM
中科院分区：
文献类型：
--
作者：
Onufriev, A;Case, DA;Ullmann, GM
当一个分子中的各个可滴定位置相互作用时，它们的pH滴定可能比经典的Henderson-Hasselbalch方程所描述的独立位置的pH滴定要复杂得多。我们提出了一个新的框架，将任何复杂的滴定行为分解成简单的标准成分。该方法将分子中的N个相互作用位点集映射到一组N个独立的、不相互作用的准位位上，每个位点用一个pK(A)‘值来表征。分子中单个位置的滴定曲线是对应于准位置的Henderson-Hasselbalch曲线的加权和。总质子化曲线是这些Henderson-Hasselbalch曲线的未加权和。我们发现，pK(A)‘值对应于可用于评估总质子吸收或释放的方法中可用的去质子化常数，并建立它们与由核磁共振或红外光谱获得的单个残基的质子化曲线之间的联系。在小分子二乙三胺五乙酸酯(DTPA)上测试了新的框架，呈现出非单调的滴定曲线，与实验数据非常吻合。我们证明，如果已知一组相互作用的一组位置中的其他位置的滴定曲线，则可以准确地重建该位置的滴定曲线。将新框架应用于蛋白质Rubredosin，证明了其在计算和解释复杂滴定曲线方面的有效性。
When individual titratable sites in a molecule interact with each other, their pH titration can be considerably more complex than that of an independent site described by the classical Henderson-Hasselbalch equation. We propose a novel framework that decomposes any complex titration behavior into simple standard components. The approach maps the set of N interacting sites in the molecule onto a set of N independent, noninteracting quasi-sites, each characterized by a pK(a)' value. The titration curve of an individual site in the molecule is a weighted sum of Henderson-Hasselbalch curves corresponding to the quasi-sites. The total protonation curve is the unweighted sum of these Henderson-Hasselbalch curves. We show that pK(a)' values correspond to deprotonation constants available from methods that can be used to assess total proton uptake or release, and establish their connection to protonation curves of individual residues obtained by NMR or infrared spectroscopy. The new framework is tested on a small molecule diethylenetriaminepentaacetate (DTPA) exhibiting nonmonotonic titration curves, where it gives an excellent fit to experimental data. We demonstrate that the titration curve of a site in a group of interacting sites can be accurately reconstructed, if titration curves of the other sites are known. The application of the new framework to the protein rubredoxin demonstrates its usefulness in calculating and interpreting complicated titration curves.