Psychrophily and catalysis.
Psychrophily and catalysis.
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DOI：
10.3390/biology2020719
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发表时间：
2013-04-16
期刊：
影响因子：
4.2
通讯作者：
Gerday C
中科院分区：
文献类型：
--
作者：
Gerday C
极地和其他低温环境的特点是能量含量低，这一因素对居住在这些相当常见的栖息地的生物有很大的影响。事实上，低温对外温生物种群具有负面影响，因为它们可以影响它们的生长、生化反应的反应速率、膜通透性、扩散速率、动作电位、蛋白质折叠、核酸动力学和其他依赖温度的生化过程。自从发现这些生态系统与最初的预期相反，维持着相当高的密度和广泛的生物多样性以来，越来越多的努力致力于了解它们成功适应明显不利的物理条件所涉及的分子机制。人们想到的第一个问题是：当温度降低时，这些生物体如何弥补反应速度的指数下降？由于生物体中发生的大多数化学反应都是由酶催化的，因此人们已经研究了冷适应酶的动力学和热力学性质。目前，这些酶的许多晶体结构已经被阐明，并允许相当清楚地看到它们对寒冷的适应。它们的特点是在中低温下具有较高的比活性和较低的热稳定性，这导致了较高的柔韧性，防止了低温对结构动力学的冻结效应。这些酶还表现出较低的激活热，使它们对温度波动的依赖性较小。这伴随着较大的活化熵负值，从而提供了更无序的基态的证据。适当的折叠动力学显然是通过大量表达触发因子和肽基-脯氨基顺式/反式异构酶来确保的。
Polar and other low temperature environments are characterized by a low content in energy and this factor has a strong incidence on living organisms which populate these rather common habitats. Indeed, low temperatures have a negative effect on ectothermic populations since they can affect their growth, reaction rates of biochemical reactions, membrane permeability, diffusion rates, action potentials, protein folding, nucleic acids dynamics and other temperature-dependent biochemical processes. Since the discovery that these ecosystems, contrary to what was initially expected, sustain a rather high density and broad diversity of living organisms, increasing efforts have been dedicated to the understanding of the molecular mechanisms involved in their successful adaptation to apparently unfavorable physical conditions. The first question that comes to mind is: How do these organisms compensate for the exponential decrease of reaction rate when temperature is lowered? As most of the chemical reactions that occur in living organisms are catalyzed by enzymes, the kinetic and thermodynamic properties of cold-adapted enzymes have been investigated. Presently, many crystallographic structures of these enzymes have been elucidated and allowed for a rather clear view of their adaptation to cold. They are characterized by a high specific activity at low and moderate temperatures and a rather low thermal stability, which induces a high flexibility that prevents the freezing effect of low temperatures on structure dynamics. These enzymes also display a low activation enthalpy that renders them less dependent on temperature fluctuations. This is accompanied by a larger negative value of the activation entropy, thus giving evidence of a more disordered ground state. Appropriate folding kinetics is apparently secured through a large expression of trigger factors and peptidyl–prolyl cis/trans-isomerases.