Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, Uttar Pradesh, India.
Phys Chem Chem Phys. 2023 Dec 6;25(47):32602-32612. doi: 10.1039/d3cp03357k.
The mechanism of protein stabilization by osmolytes remains one of the most important and long-standing puzzles. The traditional explanation of osmolyte-induced stability through the preferential exclusion of osmolytes from the protein surface has been seriously challenged by the observations like the concentration-dependent reversal of osmolyte-induced stabilization/destabilization. The more modern explanation of protein stabilization/destabilization by osmolytes considers an indirect effect due to osmolyte-induced distortion of the water structure. It provides a general mechanism, but there are numerous examples of protein-specific effects, , a particular osmolyte might stabilize one protein, but destabilize the other, that could not be rationalized through such an explanation. Herein, we hypothesized that osmolyte-induced modulation of associated water might be a critical factor in controlling protein stability in such a medium. Taking different osmolytes and papain as a protein, we proved that our proposal could explain protein stability in osmolyte media. Stabilizing osmolytes rigidify associated water structures around the protein, whereas destabilizing osmolytes make them flexible. The strong correlation between the stability and the associated water dynamics, and the fact that such dynamics are very much protein specific, established the importance of considering the modulation of associated water structures in explaining the osmolyte-induced stabilization/destabilization of proteins. More interestingly, we took another protein, bromelain, for which a traditionally stabilizing osmolyte, sucrose, acts as a stabilizer at higher concentrations but as a destabilizer at lower concentrations. Our proposal successfully explains such observations, which is probably impossible by any known mechanisms. We believe this report will trigger much research in this area.
渗透压稳定剂稳定蛋白质的机制仍然是最重要和最持久的难题之一。渗透压稳定剂通过优先将渗透压从蛋白质表面排除从而诱导蛋白质稳定的传统解释受到了严重挑战，因为观察到渗透压稳定剂诱导的稳定/不稳定作用会随浓度变化而反转。渗透压稳定剂诱导蛋白质稳定/不稳定的更现代解释认为，这种稳定/不稳定作用是由于渗透压诱导的水分子结构变形的间接效应。该解释提供了一种普遍机制，但有许多蛋白质特异性效应的例子，例如，一种特定的渗透压可能稳定一种蛋白质，但使另一种蛋白质不稳定，这种情况无法通过这种解释来合理化。在此，我们假设渗透压诱导的结合水的调节可能是控制蛋白质在这种介质中稳定性的关键因素。我们以不同的渗透压稳定剂和木瓜蛋白酶为例，证明了我们的假设可以解释渗透压稳定剂介质中蛋白质的稳定性。稳定的渗透压稳定剂使蛋白质周围的结合水结构变得僵硬，而不稳定的渗透压稳定剂使它们变得灵活。稳定性和结合水动力学之间的强相关性，以及这种动力学非常具有蛋白质特异性的事实，确立了在解释渗透压稳定剂诱导的蛋白质稳定/不稳定时考虑结合水结构调节的重要性。更有趣的是，我们选择了另一种蛋白质，菠萝蛋白酶，对于这种蛋白质，传统的稳定型渗透压稳定剂蔗糖在较高浓度下作为稳定剂，但在较低浓度下作为失稳剂。我们的假设成功地解释了这些观察结果，这可能是任何已知机制都无法解释的。我们相信，这一发现将引发该领域的大量研究。
