Knotts Thomas A, Rathore Nitin, de Pablo Juan J
Department of Chemical Engineering, Brigham Young University, Provo, Utah, USA.
Biophys J. 2008 Jun;94(11):4473-83. doi: 10.1529/biophysj.107.123158. Epub 2008 Mar 7.
The interaction of proteins with surfaces regulates numerous processes in nature, science, and technology. In many applications, it is desirable to place proteins on surfaces in an active state, and tethering represents one manner in which to accomplish this. However, a clear understanding of how tether placement and design affects protein activity is lacking. Available theoretical models predict that proteins will be stabilized when tethered to substrates. Such models suggest that the surface reduces the number of states accessible to the unfolded state of the protein, thereby reducing the entropic cost of folding on the surface compared to the bulk case. Recent studies, however, have shown that this stabilization is not always seen. The purpose of this article is to determine the validity of the theory with a thorough thermodynamic analysis of the folding of peptides attached to surfaces. Configuration-temperature-density-of-states Monte Carlo simulations are used to examine the behavior of four different peptides of different secondary and tertiary structure. It is found that the surface does reduce the entropic cost of folding for tethered peptides, as the theory suggests. This effect, however, does not always translate into improved stability because the surface may also have a destabilizing enthalpic effect. The theory neglects this effect and assumes that the enthalpy of folding is the same on and off the surface. Both the enthalpic and entropic contributions to the stability are found to be topology- and tether-placement-specific; we show that stability cannot be predicted a priori. A detailed analysis of the folding of protein A shows how the same protein can be both stabilized and destabilized on a surface depending upon how the tethering enhances or hinders the ability of the peptide to form correct tertiary structures.
蛋白质与表面的相互作用在自然界、科学和技术中调节着众多过程。在许多应用中，希望将蛋白质以活性状态放置在表面上，而拴系是实现这一目标的一种方式。然而，目前尚缺乏对拴系位置和设计如何影响蛋白质活性的清晰理解。现有的理论模型预测，蛋白质拴系到底物上时会得到稳定。这些模型表明，表面减少了蛋白质未折叠状态可及的状态数，从而与本体情况相比降低了在表面折叠的熵成本。然而，最近的研究表明，这种稳定性并非总是能观察到。本文的目的是通过对附着在表面的肽折叠进行全面的热力学分析来确定该理论的有效性。使用构型 - 温度 - 态密度蒙特卡罗模拟来研究四种具有不同二级和三级结构的不同肽的行为。结果发现，正如理论所表明的，表面确实降低了拴系肽折叠的熵成本。然而，这种效应并不总是转化为稳定性的提高，因为表面也可能具有使焓不稳定的效应。该理论忽略了这种效应，并假设表面上和表面外的折叠焓是相同的。发现对稳定性的焓和熵贡献都是拓扑结构和拴系位置特异性的；我们表明稳定性不能先验预测。对蛋白A折叠的详细分析表明，取决于拴系如何增强或阻碍肽形成正确三级结构的能力，同一蛋白质在表面上既可以得到稳定也可以变得不稳定。
