Roovers Martine, Wouters Johan, Bujnicki Janusz M, Tricot Catherine, Stalon Victor, Grosjean Henri, Droogmans Louis
Laboratoire de Microbiologie, Université Libre de Bruxelles, Belgium.
Nucleic Acids Res. 2004 Jan 22;32(2):465-76. doi: 10.1093/nar/gkh191. Print 2004.
The modified nucleoside 1-methyladenosine (m(1)A) is found in the T-loop of many tRNAs from organisms belonging to the three domains of life (Eukaryota, Bacteria, Archaea). In the T-loop of eukaryotic and bacterial tRNAs, m(1)A is present at position 58, whereas in archaeal tRNAs it is present at position(s) 58 and/or 57, m(1)A57 being the obligatory intermediate in the biosynthesis of 1-methylinosine (m(1)I57). In yeast, the formation of m(1)A58 is catalysed by the essential tRNA (m(1)A58) methyltransferase (MTase), a tetrameric enzyme that is composed of two types of subunits (Gcd14p and Gcd10p), whereas in the bacterium Thermus thermophilus the enzyme is a homotetramer of the TrmI polypeptide. Here, we report that the TrmI enzyme from the archaeon Pyrococcus abyssi is also a homotetramer. However, unlike the bacterial site-specific TrmI MTase, the P.abyssi enzyme is region-specific and catalyses the formation of m(1)A at two adjacent positions (57 and 58) in the T-loop of certain tRNAs. The stabilisation of P.abyssi TrmI at extreme temperatures involves intersubunit disulphide bridges that reinforce the tetrameric oligomerisation, as revealed by biochemical and crystallographic evidences. The origin and evolution of m(1)A MTases is discussed in the context of different hypotheses of the tree of life.
修饰核苷1 - 甲基腺苷（m(1)A）存在于来自生命三域（真核生物、细菌、古菌）的许多生物体的tRNA的T环中。在真核生物和细菌tRNA的T环中，m(1)A存在于第58位，而在古菌tRNA中，它存在于第58位和/或第57位，m(1)A57是1 - 甲基肌苷（m(1)I57）生物合成中的必需中间体。在酵母中，m(1)A58的形成由必需的tRNA（m(1)A58）甲基转移酶（MTase）催化，该酶是一种由两种亚基（Gcd14p和Gcd10p）组成的四聚体酶，而在嗜热栖热菌中，该酶是TrmI多肽的同四聚体。在这里，我们报道来自深渊嗜热栖热菌的TrmI酶也是同四聚体。然而，与细菌位点特异性TrmI MTase不同，深渊嗜热栖热菌的酶是区域特异性的，可催化某些tRNA的T环中两个相邻位置（57和58）处m(1)A的形成。生化和晶体学证据表明，深渊嗜热栖热菌TrmI在极端温度下的稳定性涉及亚基间二硫键，这些二硫键加强了四聚体寡聚化。本文在不同生命树假说的背景下讨论了m(1)A MTases的起源和进化。
