It is well established that any properly conducted biophysical studies of proteins must take appropriate account of solvent. For water-soluble proteins it has been an article of faith that water is largely responsible for stabilizing the fold, a notion that has recently come under increasing scrutiny. Further, there are some instances when proteins are studied experimentally in the absence of solvent, as in matrix-assisted laser desorption/ionization or electrospray mass spectrometry, for example, or in organic solvents for protein engineering purposes. Apart from these considerations, there is considerable speculation as to whether there is life on planets other than Earth, where conditions including the presence of water (both in liquid or vapour form and indeed ice), temperature and pressure may be vastly different from those prevailing on Earth. Mars, for example, has only 0.6% of Earth's mean atmospheric pressure which presents profound problems to protein structures, as this paper and a large corpus of experimental work demonstrate. Similar objections will most likely apply in the case of most exoplanets and other bodies such as comets whose chemistry and climate are still largely unknown.This poses the question, how do proteins survive in these different environments? In order to cast some light on these issues we have conducted a series of molecular dynamics simulations on protein dehydration under a variety of conditions. We find that, while proteins undergoing dehydration can retain their integrity for a short duration they ultimately become disordered, and we further show that the disordering can be retarded if superficial water is kept in place on the surface. These findings are compared with other published results on protein solvation in an astrobiological and astrochemical setting. Inter alia, our results suggest that there are limits as to what to expect in terms of the existence of possible extraterrestrial forms as well to what can be achieved in experimental investigations on living systems despatched from Earth. This finding may appear to undermine currently held hopes that life will be found on nearby planets, but it is important to be aware that the presence of ice and water are by themselves not sufficient; there has to be an atmosphere which includes water vapour at a sufficiently high partial pressure for proteins to be active. A possible scenario in which there has been a history of adequate water vapour pressure which allowed organisms to prepare for a future desiccated state by forming suitable protective capsules cannot of course be ruled out.

中文翻译：

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蛋白质在外太空的命运

众所周知，任何适当进行的蛋白质生物物理研究都必须适当考虑溶剂。对于水溶性蛋白质来说，水主要负责稳定折叠一直是一种信念，这一概念最近受到越来越多的审查。此外，在某些情况下，在没有溶剂的情况下对蛋白质进行实验研究，例如在基质辅助激光解吸/电离或电喷雾质谱中，或在用于蛋白质工程目的的有机溶剂中。除了这些考虑之外，还有很多关于地球以外的行星上是否存在生命的推测，其中包括水的存在（液体或蒸汽形式，实际上是冰）的存在，温度和压力可能与地球上普遍存在的大不相同。例如，火星只有地球平均大气压力的 0.6%，这对蛋白质结构提出了深刻的问题，正如本文和大量实验工作所证明的那样。类似的反对意见很可能适用于大多数系外行星和其他天体，如彗星，它们的化学和气候在很大程度上仍然未知。这就提出了一个问题，蛋白质如何在这些不同的环境中生存？为了阐明这些问题，我们对各种条件下的蛋白质脱水进行了一系列分子动力学模拟。我们发现，虽然经历脱水的蛋白质可以在短时间内保持其完整性，但它们最终会变得无序，我们进一步表明，如果表面水保持在适当的位置，可以减缓无序化。这些发现与其他已发表的关于天体生物学和天体化学环境中蛋白质溶剂化的结果进行了比较。除其他外，我们的研究结果表明，就可能存在的外星形式的存在以及对从地球派遣的生命系统的实验研究可以实现的目标而言，存在限制。这一发现似乎破坏了目前对在附近行星上发现生命的希望，但重要的是要意识到冰和水的存在本身是不够的；必须有一种包含水蒸气且分压足够高的气氛，蛋白质才能发挥作用。