Crowe J H, Carpenter J F, Crowe L M
Section of Molecular and Cellular Biology, University of California, Davis 95616, USA.
Annu Rev Physiol. 1998;60:73-103. doi: 10.1146/annurev.physiol.60.1.73.
Numerous organisms are capable of surviving more or less complete dehydration. A common feature in their biochemistry is that they accumulate large amounts of disaccharides, the most common of which are sucrose and trehalose. Over the past 20 years, we have provided evidence that these sugars stabilize membranes and proteins in the dry state, most likely by hydrogen bonding to polar residues in the dry macromolecular assemblages. This direct interaction results in maintenance of dry proteins and membranes in a physical state similar to that seen in the presence of excess water. An alternative viewpoint has been proposed, based on the fact that both sucrose and trehalose form glasses in the dry state. It has been suggested that glass formation (vitrification) is in itself sufficient to stabilize dry biomaterials. In this review we present evidence that, although vitrification is indeed required, it is not in itself sufficient. Instead, both direct interaction and vitrification are required. Special properties have often been claimed for trehalose in this regard. In fact, trehalose has been shown by many workers to be remarkably (and sometimes uniquely) effective in stabilizing dry or frozen biomolecules, cells, and tissues. Others have not observed any such special properties. We review evidence here showing that trehalose has a remarkably high glass-transition temperature (Tg). It is not anomalous in this regard because it lies at the end of a continuum of sugars with increasing Tg. However, it is unusual in that addition of small amounts of water does not depress Tg, as in other sugars. Instead, a dihydrate crystal of trehalose forms, thereby shielding the remaining glassy trehalose from effects of the added water. Thus under less than ideal conditions such as high humidity and temperature, trehalose does indeed have special properties, which may explain the stability and longevity of anhydrobiotes that contain it. Further, it makes this sugar useful in stabilization of biomolecules of use in human welfare.
许多生物体能够或多或少地在完全脱水的状态下存活。它们生物化学中的一个共同特征是积累大量的二糖，其中最常见的是蔗糖和海藻糖。在过去的20年里，我们已经提供了证据表明，这些糖类在干燥状态下能稳定膜和蛋白质，最有可能是通过与干燥大分子集合体中的极性残基形成氢键。这种直接相互作用使得干燥的蛋白质和膜保持在一种类似于在过量水存在时的物理状态。基于蔗糖和海藻糖在干燥状态下都会形成玻璃态这一事实，有人提出了另一种观点。有人认为玻璃态的形成（玻璃化）本身就足以稳定干燥的生物材料。在这篇综述中，我们提供的证据表明，虽然玻璃化确实是必需的，但它本身并不足够。相反，直接相互作用和玻璃化都是必需的。在这方面，人们常常声称海藻糖具有特殊性质。事实上，许多研究人员已经表明，海藻糖在稳定干燥或冷冻的生物分子、细胞和组织方面非常有效（有时甚至是独特的有效）。其他人则没有观察到任何这样的特殊性质。我们在这里综述的证据表明，海藻糖具有非常高的玻璃化转变温度（Tg）。在这方面它并非异常，因为它处于随着Tg升高的一系列糖类的末端。然而，它不同寻常之处在于，与其他糖类不同，加入少量水并不会降低Tg。相反，会形成海藻糖二水合物晶体，从而使剩余的玻璃态海藻糖免受添加水的影响。因此，在湿度和温度较高等不太理想的条件下，海藻糖确实具有特殊性质，这可能解释了含有它的脱水生物的稳定性和寿命。此外，这使得这种糖在稳定对人类有益的生物分子方面很有用。
