XRAY CRYSTAL STRUCTURE DETERMINATION OF RUVB DNA HELICASE

收集了细菌四氢呋喃晶体的数据， 1996年5月在CHESS光束线A-1上六聚RuvB DNA解旋酶。 这些 晶体属于空间群P41212（或对映体P43212） 具有晶胞参数a = B = 86.7
，c = 362.5
，a = B = g = 900. 溶剂含量计算和计算的 自旋转函数与三个分子一致， 不对称单元，总溶剂含量为62%。 最优 结晶条件产生尺寸为0.7mm × 0.4mm × 0.5mm的晶体。 0.4低温溶剂成功地用于快速冷却这些晶体 用于数据收集，分辨率为3.6
.非晶体学的 对原生数据集的对称计算与 模型表明，六聚体解旋酶，如细菌 Rho RNA解旋酶，采用D3点群对称， 环中的每一个分子都指向相反的方向。 更确切地说，他们认为环使顶部朝向同一方向， 的方面想 值得注意的是，RuvB的构象不是六重的， 对称的，而是三重对称的。 这是其中一个州 观察DnaB解旋酶的电子显微镜，并建议 晶体代表了两种交替构象之一， 解旋酶在反应周期中的作用。

Data was collected on tetragonal crystals of the bacterial hexameric RuvB DNA helicase in May 1996 at CHESS beam line A-1. These crystals are in the space group P41212 (or the enantiomorph P43212) with unit cell parameters a = b = 86.7
, c = 362.5
, a = b = g = 900. The solvent content calculations and the calculated self-rotation function are consistent with three molecules in the asymmetric unit for an overall solvent content of 62%. Optimal crystallization conditions produce crystals of size 0.7 mm x 0.4 mm x 0.4 mm. A cryosolvent was successful for flash cooling these crystals for data collection to a resolution of 3.6
. Non-crystallographic symmetry calculations on the native data set are inconsistent with models that suggest that hexameric helicases, such as the bacterial Rho RNA helicase, adopt a D3 point group symmetry with the tops of every other molecule in the ring points in an opposite direction. Rather, they suggest that the ring orients the tops towards the same side. Significantly, the conformation of RuvB is not six-fold symmetric, but rather three-fold symmetric. This is one of the states observed for the DnaB helicase by electron microscopy and suggests that the crystals represent one of two alternate conformations of the helicase during the reaction cycle.