STRUCTURAL THEMODYNAMICS OF A HYPERTHERMOPHILE

超嗜热蛋白在结构生物学中具有特殊的意义，因为它们被设计为在生命的最高温度下发挥作用(即。80至110摄氏度)。这项工作的长期目标是利用超嗜热蛋白质的独特属性来增加我们对蛋白质能量学的理解，并增强我们在蛋白质工程和生物技术方面的能力。这些蛋白质不仅对于如何以合理的方式控制稳定性提供线索，而且对于扩大可用于研究蛋白质折叠和结合等蛋白质过程的条件的实验范围也是重要的。在这项工作中，我们建议利用两种超嗜热蛋白质的高热稳定性和酸稳定性来定量描述离子相互作用在折叠中的重要性，以及在蛋白质-DNA结合中扭曲DNA的能量成本。许多超嗜热蛋白质的结构现在是可用的，这些数据已经被用来为这些蛋白质在高温下增强稳定性和功能提出合理的解释。最常见的解释是更多的离子对，预计它们在高温下将变得越来越重要。对于所提出的离子对相互作用在这些蛋白质中的相对重要性，很少有深入的热力学研究，也没有实验证明预测的温度相关性。7kD染色质蛋白Sac7d和Sso7d已被证明是研究稳定性的理想嗜热蛋白。考虑到离子对的高密度和我们在各种条件下定义这些蛋白质稳定性的能力，它们是研究超嗜热蛋白质中离子相互作用的重要性和行为的理想工具。Sac7d和Sso7d还为蛋白质-DNA结合的能量学研究提供了相对简单的模型系统，因为它们在DNA中引起了观察到的任何蛋白质最大的扭结之一。这里将利用高热稳定性来定义宽温度范围内DNA结合和弯曲的能量学，以可靠地分离折叠、结合和弯曲的影响。这些相互作用将通过扫描和滴定量热法、核磁共振、定点突变、圆二色谱和小角X射线散射相结合的方法进行研究。从这个项目中获得的信息将有助于我们以合理的方式设计和控制蛋白质稳定性和蛋白质-DNA相互作用的能力，并有可能在医学和生物技术中应用。

Hyperthermophile proteins are of special interest in structural biology since they are designed to function at the upper temperature limit of life (viz. 80 to 110 degrees C). The long term goal of this work is to utilize the unique attributes of hyperthermophile proteins to increase our understanding of protein energetics and enhance our capabilities in protein engineering and biotechnology. These proteins are important not only for providing clues on how to control stability in a rational manner, but also for expanding the experimental range of conditions available for investigating protein processes such as folding and binding. In this work we propose to take advantage of the high thermal and acid stability of two hyperthermophile proteins to quantitatively describe the importance of ionic interactions in folding and the energetic cost of distorting DNA in protein-DNA binding. The structures of a number of hyperthermophile proteins are now available, and this data has been utilized to propose rational explanations for enhanced stability and function in these proteins at high temperature. The most common explanation is a greater number of ion pairs, which are expected to be increasingly important at high temperature. There have been few in-depth thermodynamic studies of the relative importance of the proposed ion pair interactions in these proteins and no experimental demonstration of the predicted temperature dependence. The 7 kD chromatin proteins Sac7d and Sso7d have proven to be ideal hyperthermophile proteins for studies of stability. Given a high density of ion pairs and our ability to define the stabilities of these proteins over a wide range of conditions, they are ideal for studies of the importance and behavior of ionic interactions in hyperthermophile proteins. Sac7d and Sso7d also provide relatively simple model systems for studies of the energetics of protein-DNA binding since they induce one of the largest kinks in DNA observed for any protein. The high thermal stability will be utilized here to define the energetics of DNA binding and bending over a wide temperature range to reliably separate the effects of folding, binding and bending. These interactions will be investigated by a combination of scanning and titration calorimetry, NMR, site-directed mutagenesis, circular dichroism, and small-angle X- ray scattering. Information gained from this project will contribute to our ability to design and control protein stability and protein-DNA interactions in a rational manner with potential applications in medicine and biotechnology.