School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, United Kingdom.
Biochemistry. 2014 May 6;53(17):2855-63. doi: 10.1021/bi500238q. Epub 2014 Apr 22.
The thermal melting temperature of dihydrofolate reductase from Geobacillus stearothermophilus (BsDHFR) is ~30 °C higher than that of its homologue from the psychrophile Moritella profunda. Additional proline residues in the loop regions of BsDHFR have been proposed to enhance the thermostability of BsDHFR, but site-directed mutagenesis studies reveal that these proline residues contribute only minimally. Instead, the high thermal stability of BsDHFR is partly due to removal of water-accessible thermolabile residues such as glutamine and methionine, which are prone to hydrolysis or oxidation at high temperatures. The extra thermostability of BsDHFR can be obtained by ligand binding, or in the presence of salts or cosolvents such as glycerol and sucrose. The sum of all these incremental factors allows BsDHFR to function efficiently in the natural habitat of G. stearothermophilus, which is characterized by temperatures that can reach 75 °C.
嗜热脂肪地芽孢杆菌二氢叶酸还原酶（BsDHFR）的热融解温度比其来自嗜冷菌深海栖热袍菌的同源物高约 30°C。据推测，BsDHFR 环区中的额外脯氨酸残基可以增强其热稳定性，但定点突变研究表明，这些脯氨酸残基的贡献很小。相反，BsDHFR 的高热稳定性部分归因于去除了可接触水的热敏不稳定残基，如谷氨酰胺和蛋氨酸，这些残基在高温下容易发生水解或氧化。配体结合，或在盐或甘油和蔗糖等共溶剂存在下，可获得 BsDHFR 的额外热稳定性。所有这些递增因素的总和使 BsDHFR 能够在其天然栖息地——嗜热脂肪地芽孢杆菌中高效发挥作用，其特点是温度可达 75°C。
