Vieille C, Burdette D S, Zeikus J G
Department of Biochemistry, Michigan State University, East Lansing 48909, USA.
Biotechnol Annu Rev. 1996;2:1-83. doi: 10.1016/s1387-2656(08)70006-1.
Enzymes synthesized by thermophiles (organisms with optimal growth temperatures > 60 degrees C) and hyperthermophiles (optimal growth temperatures > 80 degrees C) are typically thermostable (resistant to irreversible inactivation at high temperatures) and thermophilic (optimally active at high temperatures, i.e., > 60 degrees C). These enzymes, called thermozymes, share catalytic mechanisms with their mesophilic counterparts. When cloned and expressed in mesophilic hosts, thermozymes usually retain their thermal properties, suggesting that these properties are genetically encoded. Sequence alignments, amino acid content comparisons, and crystal structure comparisons indicate that thermozymes are, indeed, very similar to mesophilic enzymes. No obvious sequence or structural features account for enzyme thermostability and thermophilicity. Thermostability and thermophilicity molecular mechanisms are varied, differing from enzyme to enzyme. Thermostability and thermophilicity are usually caused by the accumulation of numerous subtle sequence differences. This review concentrates on the mechanisms involved in enzyme thermostability and thermophilicity. Their relationships with protein rigidity and flexibility and with protein folding and unfolding are discussed. Intrinsic stabilizing forces (e.g., salt bridges, hydrogen bonds, hydrophobic interactions) and extrinsic stabilizing factors are examined. Finally, thermozymes' potential as catalysts for industrial processes and specialty uses are discussed, and lines of development (through new applications, and protein engineering) are also proposed.
嗜热菌（最佳生长温度>60摄氏度的生物体）和超嗜热菌（最佳生长温度>80摄氏度）合成的酶通常具有热稳定性（在高温下抗不可逆失活）和嗜热性（在高温下，即>60摄氏度时具有最佳活性）。这些酶被称为嗜热酶，与它们的嗜温对应物具有相同的催化机制。当在嗜温宿主中克隆和表达时，嗜热酶通常保留其热性质，这表明这些性质是由基因编码的。序列比对、氨基酸含量比较和晶体结构比较表明，嗜热酶确实与嗜温酶非常相似。没有明显的序列或结构特征可以解释酶的热稳定性和嗜热性。热稳定性和嗜热性的分子机制各不相同，因酶而异。热稳定性和嗜热性通常是由众多细微的序列差异积累引起的。本综述集中讨论了酶热稳定性和嗜热性所涉及的机制。讨论了它们与蛋白质刚性和柔韧性以及与蛋白质折叠和去折叠的关系。研究了内在稳定力（如盐桥、氢键、疏水相互作用）和外在稳定因素。最后，讨论了嗜热酶作为工业过程和特殊用途催化剂的潜力，并提出了发展方向（通过新应用和蛋白质工程）。
