Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore.
FEBS Lett. 2011 Oct 3;585(19):3126-32. doi: 10.1016/j.febslet.2011.08.048. Epub 2011 Sep 6.
Insoluble proteins dissolved in unsalted water appear to have no well-folded tertiary structures. This raises a fundamental question as to whether being unstructured is due to the absence of salt ions. To address this issue, we solubilized the insoluble ephrin-B2 cytoplasmic domain in unsalted water and first confirmed using NMR spectroscopy that it is only partially folded. Using NMR HSQC titrations with 14 different salts, we further demonstrate that the addition of salt triggers no significant folding of the protein within physiologically relevant ion concentrations. We reveal however that their 8 anions bind to the ephrin-B2 protein with high affinity and specificity at biologically-relevant concentrations. Interestingly, the binding is found to be both salt- and residue-specific.
不溶性蛋白质溶解在无盐水中似乎没有良好折叠的三级结构。这就提出了一个基本问题，即无结构是否是由于没有盐离子。为了解决这个问题，我们将不溶性的 Ephrin-B2 胞质结构域溶解在无盐水中，并首先使用 NMR 光谱证实它只是部分折叠的。通过与 14 种不同盐的 NMR HSQC 滴定实验，我们进一步证明在生理相关的离子浓度下，盐的添加不会引发蛋白质的显著折叠。然而，我们揭示了它们的 8 种阴离子在生物相关浓度下以高亲和力和特异性结合到 Ephrin-B2 蛋白上。有趣的是，这种结合既具有盐依赖性，也具有残基特异性。
