Reshetnikova L, Chernaya M, Ankilova V, Lavrik O, Delarue M, Thierry J C, Moras D, Safro M
Institute of Molecular Biology, Academy of Sciences of the USSR, Moscow.
Eur J Biochem. 1992 Sep 1;208(2):411-7. doi: 10.1111/j.1432-1033.1992.tb17202.x.
The three-dimensional structure of the heterodimeric alpha 2 beta 2 enzyme phenylalanyl-tRNA synthetase from Thermus thermophilus HB8 has been determined by X-ray crystallography, using the multiple-isomorphous-replacement method at 0.6 nm resolution. Trigonal crystals of space group P3(2)21 have cell dimensions a = b = 17.6 nm and c = 14.2 nm. Assuming one heterodimeric molecule/asymmetric unit, the ratio of unit cell volume/molecular mass was V = 0.00244 nm3/Da, which is in the middle of the range normally observed. However, after a rotation-function calculation and measurement of the density of the native crystals, we postulate the existence of only the alpha beta dimer in the asymmetric units. This implies 73% solvent content in the unit cell. Three heavy-atom derivatives [K2PtCl4, KAu(CN)2 and Hg(CH3COO)2] and the solvent-flattening procedure were used for electron-density-map calculations. This map confirmed our hypothesis and revealed a remarkably large space filled by solvent, with alpha beta dimer only in the asymmetric unit. The phenylalanyl-tRNA synthetase from T. thermophilus molecule has a 'quasi-linear' subunit organization. As can be concluded at this level of resolution, there is no contact between small alpha subunits in the functional heterodimer.
嗜热栖热菌HB8的异源二聚体α2β2苯丙氨酰 - tRNA合成酶的三维结构已通过X射线晶体学确定，采用多重同晶置换法，分辨率为0.6纳米。空间群为P3(2)21的三方晶体，晶胞尺寸a = b = 17.6纳米，c = 14.2纳米。假设一个异源二聚体分子/不对称单位，晶胞体积与分子量之比为V = 0.00244纳米3/道尔顿，处于正常观察范围的中间。然而，在进行旋转函数计算并测量天然晶体的密度后，我们推测不对称单位中仅存在αβ二聚体。这意味着晶胞中溶剂含量为73%。使用三种重原子衍生物[K2PtCl4、KAu(CN)2和Hg(CH3COO)2]以及溶剂扁平化程序进行电子密度图计算。该图证实了我们的假设，并揭示了一个由溶剂占据的非常大的空间，不对称单位中仅有αβ二聚体。嗜热栖热菌的苯丙氨酰 - tRNA合成酶分子具有“准线性”亚基组织。在这个分辨率水平上可以得出结论，功能性异源二聚体中的小α亚基之间没有接触。
