Lee Charles K, Cary S Craig, Murray Alison E, Daniel Roy M
Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand.
Appl Environ Microbiol. 2008 Feb;74(3):774-82. doi: 10.1128/AEM.01960-07. Epub 2007 Dec 14.
The equilibrium model, which describes the influence of temperature on enzyme activity, has been established as a valid and useful tool for characterizing enzyme eurythermalism and thermophily. By introducing K(eq), a temperature-dependent equilibrium constant for the interconversion between E(act), the active form of enzyme, and E(inact), a reversibly inactive form of enzyme, the equilibrium model currently provides the most complete description of the enzyme-temperature relationship; its derived parameters are intrinsic and apparently universal and, being derived under reaction conditions, potentially have physiological significance. One of these parameters, T(eq), correlates with host growth temperature better than enzyme stability does. The vent-dwelling annelid Alvinella pompejana has been reported as an extremely eurythermal organism, and the symbiotic complex microbial community associated with its dorsal surface is likely to experience similar environmental thermal conditions. The A. pompejana episymbiont community, predominantly composed of epsilonproteobacteria, has been analyzed metagenomically, enabling direct retrieval of genes coding for enzymes suitable for equilibrium model applications. Two such genes, coding for isopropylmalate dehydrogenase and glutamate dehydrogenase, have been isolated from the A. pompejana episymbionts, heterologously expressed, and shown by reverse transcription-quantitative PCR to be actively expressed. The equilibrium model parameters of characterized expression products suggested that enzyme eurythermalism constitutes part of the thermal adaptation strategy employed by the episymbionts. Moreover, the enzymes' thermal characteristics correspond to their predicted physiological roles and the abundance and expression of the corresponding genes. This paper demonstrates the use of the equilibrium model as part of a top-down metagenomic approach to studying temperature adaptation of uncultured organisms.
平衡模型描述了温度对酶活性的影响，已被确立为表征酶的广温性和嗜热性的有效且有用的工具。通过引入K(eq)，即酶的活性形式E(act)与可逆失活形式E(inact)之间相互转化的温度依赖性平衡常数，平衡模型目前提供了对酶 - 温度关系最完整的描述；其推导参数是内在的且显然具有普遍性，并且在反应条件下得出，可能具有生理意义。其中一个参数T(eq)与宿主生长温度的相关性比酶稳定性更好。据报道，生活在热液喷口的多毛纲动物庞贝蠕虫是一种极端广温性生物，与其背面相关的共生复合微生物群落可能经历类似的环境热条件。对主要由ε-变形菌组成的庞贝蠕虫体表共生菌群落进行了宏基因组分析，能够直接检索编码适用于平衡模型应用的酶的基因。已从庞贝蠕虫体表共生菌中分离出两个这样的基因，分别编码异丙基苹果酸脱氢酶和谷氨酸脱氢酶，进行了异源表达，并通过逆转录定量PCR显示它们能活跃表达。对已表征的表达产物的平衡模型参数表明，酶的广温性构成了体表共生菌所采用热适应策略的一部分。此外，这些酶的热特性与其预测的生理作用以及相应基因的丰度和表达相对应。本文展示了平衡模型作为自上而下的宏基因组方法的一部分用于研究未培养生物的温度适应性。
