Törö Imre, Basquin Jérôme, Teo-Dreher Hiang, Suck Dietrich
Structural and Computational Biology Programme, EMBL, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
J Mol Biol. 2002 Jun 28;320(1):129-42. doi: 10.1016/S0022-2836(02)00406-0.
Proteins of largely unknown function related to the Sm proteins present in the core domain of eukaryotic small nuclear ribonucleoprotein particles have recently been detected in Archaea. In contrast to eukaryotes, Archaea contain maximally two distinct Sm-related proteins belonging to different subfamilies, we refer to as Sm1 and Sm2. Here we report the crystal structures of the Sm1- and Sm2-type proteins from the hyperthermophilic euryarchaeon Archaeoglobus fulgidus (AF-Sm1 and AF-Sm2) at a resolution of 2.5 and 1.95 A, respectively. While the AF-Sm1 protein forms a heptameric ring structure similar to that found in other archaeal Sm1-type proteins, the AF-Sm2 protein unexpectedly forms a homo-hexamer in the crystals, and, as is evident from the mass spectrometric analysis, also in solution. Both proteins have essentially the same monomer fold and inter-subunit beta-sheet hydrogen bonding giving rise to a similar overall architecture of the doughnut-shaped six and seven-membered rings. In addition, a conserved uracil-binding pocket identified previously in an AF-Sm1/RNA complex, suggests a common RNA-binding mode for the AF-Sm1 and AF-Sm2 proteins, in line with solution studies showing preferential binding to U-rich oligonucleotides for both proteins. Clear differences are however seen in the charge distribution within the two structures. The rough faces of the rings, i.e. the faces not containing the base binding pockets, have opposite charges in the two structures, being predominantly positive in AF-Sm1 and negative in AF-Sm2. Differences in the ionic interactions between subunits provide an explanation for the distinctly different oligomerisation behaviour of the AF-Sm1 and AF-Sm2 proteins and of Sm1- and Sm2-type proteins in general, as well as the stability of their complexes. Implications for the functions of archaeal Sm proteins are being discussed.
最近在古菌中检测到了与真核生物小核核糖核蛋白颗粒核心结构域中存在的Sm蛋白相关的功能 largely unknown 的蛋白质。与真核生物不同，古菌最多包含两种属于不同亚家族的不同Sm相关蛋白，我们将其称为Sm1和Sm2。在这里，我们分别以2.5 Å和1.95 Å的分辨率报告了来自嗜热广古菌嗜热栖热菌（AF-Sm1和AF-Sm2）的Sm1型和Sm2型蛋白的晶体结构。虽然AF-Sm1蛋白形成了与其他古菌Sm1型蛋白中发现的类似的七聚体环结构，但AF-Sm2蛋白在晶体中意外地形成了同六聚体，并且，从质谱分析中可以明显看出，在溶液中也是如此。两种蛋白具有基本相同的单体折叠和亚基间β-折叠氢键，从而产生了类似的甜甜圈形状的六元和七元环的整体结构。此外，先前在AF-Sm1/RNA复合物中鉴定出的保守尿嘧啶结合口袋，表明AF-Sm1和AF-Sm2蛋白具有共同的RNA结合模式，这与溶液研究结果一致，即两种蛋白都优先结合富含U的寡核苷酸。然而，在两种结构的电荷分布中可以看到明显的差异。环的粗糙面，即不包含碱基结合口袋的面，在两种结构中具有相反的电荷，在AF-Sm1中主要为正电荷，在AF-Sm2中为负电荷。亚基之间离子相互作用的差异为AF-Sm1和AF-Sm2蛋白以及一般Sm1和Sm2型蛋白明显不同的寡聚行为及其复合物的稳定性提供了解释。正在讨论古菌Sm蛋白功能的影响。
