Models of Titan predict that there is a subsurface ocean of water and ammonia under a layer of ice. Such an ocean would be important in the search for extraterrestrial life since it provides a potentially habitable environment. To evaluate how Earth-based proteins would behave in Titan's subsurface ocean environment, we used molecular dynamics simulations to calculate the properties of proteins with the most common secondary structure types (alpha helix and beta sheet) in both Earth and Titan-like conditions. The Titan environment was simulated by using a temperature of 300 K, a pressure of 1000 bar, and a eutectic mixture of water and ammonia. We analyzed protein compactness, flexibility, and backbone dihedral distributions to identify differences between the two environments. Secondary structures in the Titan environment were found to be less long-lasting, less flexible, and had small differences in backbone dihedral preferences (e.g., in one instance a pi helix formed). These environment-driven differences could lead to changes in how these proteins interact with other biomolecules and therefore changes in how evolution would potentially shape proteins to function in subsurface ocean environments.

中文翻译：

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泰坦地下水海洋中的蛋白质稳定性。

泰坦模型预测，在一层冰之下有一个水和氨的地下海洋。这样的海洋对于寻找外星生命至关重要，因为它提供了潜在的宜居环境。为了评估土生土类蛋白质在土卫六地下海洋环境中的行为，我们使用分子动力学模拟来计算在土质和土卫六条件下具有最常见二级结构类型（α螺旋和β片层）的蛋白质的特性。通过使用300 K的温度，1000 bar的压力以及水和氨的低共熔混合物来模拟Titan环境。我们分析了蛋白质的紧密度，柔韧性和主链二面体分布，以确定两种环境之间的差异。发现泰坦环境中的二级结构的持久性较差，柔韧性较低，并且骨架二面角偏好的差异较小（例如，在一个实例中形成π螺旋）。这些由环境驱动的差异可能会导致这些蛋白质与其他生物分子相互作用的方式发生变化，因此，进化方式的变化将潜在地影响蛋白质在地下海洋环境中的功能。