Forterre P, Bergerat A, Lopez-Garcia P
Institut de Génétique et Microbiologie, University Paris-Sud, CNRS, URA 1354, Orsay, France.
FEMS Microbiol Rev. 1996 May;18(2-3):237-48. doi: 10.1111/j.1574-6976.1996.tb00240.x.
Hyperthermophilic archaea exhibit a unique pattern of DNA topoisomerase activities. They have a peculiar enzyme, reverse gyrase, which introduces positive superturns into DNA at the expense of ATP. This enzyme has been found in all hyperthermophiles tested so far (including Bacteria) but never in mesophiles. Reverse gyrases are formed by the association of a helicase-like domain and a 5'-type 1 DNA topoisomerase. These two domains might be located on the same polypeptide. However, in the methanogenic archaeon Methanopyrus kandleri, the topoisomerase domain is divided between two subunits. Besides reverse gyrase, Archaea contain other type 1 DNA topoisomerases; in particular, M. kandleri harbors the only known procaryotic 3'-type 1 DNA topoisomerase (Topo V). Hyperthermophilic archaea also exhibit specific type II DNA topoisomerases (Topo II), i.e. whereas mesophilic Bacteria have a Topo II that produces negative supercoiling (DNA gyrase), the Topo II from Sulfolobus and Pyrococcus lack gyrase activity and are the smallest enzymes of this type known so far. This peculiar pattern of DNA topoisomerases in hyperthermophilic archaea is paralleled by a unique DNA topology, i.e. whereas DNA isolated from Bacteria and Eucarya is negatively supercoiled, plasmidic DNA from hyperthermophilic archaea are from relaxed to positively supercoiled. The possible evolutionary implications of these findings are discussed in this review. We speculate that gyrase activity in mesophiles and reverse gyrase activity in hyperthermophiles might have originated in the course of procaryote evolution to balance the effect of temperature changes on DNA structure.
嗜热古菌展现出独特的DNA拓扑异构酶活性模式。它们有一种特殊的酶，即反向回旋酶，该酶以ATP为代价将正超螺旋引入DNA。到目前为止，在所有测试过的嗜热菌（包括细菌）中都发现了这种酶，但在嗜温菌中从未发现。反向回旋酶由一个解旋酶样结构域和一个5'-1型DNA拓扑异构酶结合形成。这两个结构域可能位于同一多肽上。然而，在产甲烷古菌坎氏甲烷球菌中，拓扑异构酶结构域分布在两个亚基之间。除了反向回旋酶，古菌还含有其他1型DNA拓扑异构酶；特别是，坎氏甲烷球菌含有唯一已知的原核3'-1型DNA拓扑异构酶（拓扑异构酶V）。嗜热古菌还展现出特定的II型DNA拓扑异构酶（拓扑异构酶II），即嗜温细菌有一种产生负超螺旋的拓扑异构酶II（DNA回旋酶），而来自硫化叶菌属和火球菌属的拓扑异构酶II缺乏回旋酶活性，是迄今为止已知的该类型中最小的酶。嗜热古菌中这种独特的DNA拓扑异构酶模式与独特的DNA拓扑结构相对应，即从细菌和真核生物中分离出的DNA是负超螺旋的，而嗜热古菌的质粒DNA从松弛到正超螺旋。本综述讨论了这些发现可能的进化意义。我们推测，嗜温菌中的回旋酶活性和嗜热菌中的反向回旋酶活性可能起源于原核生物进化过程中，以平衡温度变化对DNA结构的影响。
