It has been suggested that structural rigidity is connected to thermostability, e.g. in enzymes from thermophilic microorganisms. We examine the importance of correctly handling salt bridges, and interactions which we term 'strong polars', when constructing the constraint network for global rigidity analysis in these systems. Through a comparison of rigidity in citrate synthases, we clarify the relationship between rigidity and thermostability. In particular, with our corrected handling of strong polar interactions, the difference in rigidity between mesophilic and thermophilic structures is detected more clearly than in previous studies. The increase in rigidity did not detract from the functional flexibility of the active site in all systems once their respective temperature range had been reached. We then examine the distribution of salt bridges in thermophiles that were previously unaccounted for in flexibility studies. We show that in hyperthermophiles these have stabilising roles in the active site; occuring in close proximity to key residues involved in catalysis and binding of the protein.

中文翻译：

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盐桥对嗜热柠檬酸合酶的整体刚性和热稳定性有影响。

已经提出结构刚性与热稳定性有关，例如在嗜热微生物的酶中。在构建用于这些系统中的全局刚度分析的约束网络时，我们研究了正确处理盐桥以及所谓的“强极性”相互作用的重要性。通过柠檬酸合酶刚性的比较，我们阐明了刚性与热稳定性之间的关系。特别是，通过我们对强极性相互作用的正确处理，比以前的研究更清楚地检测到了嗜温和嗜热结构之间的刚性差异。一旦达到各自的温度范围，刚度的增加就不会降低所有系统中活性部位的功能灵活性。然后，我们检查了灵活性研究中以前未说明的嗜热盐中盐桥的分布。我们显示在嗜热菌中，这些在活性位点具有稳定作用；发生在与蛋白质催化和结合有关的关键残基附近。