Sevcik J, Dauter Z, Lamzin V S, Wilson K S
Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovak Republic.
Acta Crystallogr D Biol Crystallogr. 1996 Mar 1;52(Pt 2):327-44. doi: 10.1107/S0907444995007669.
Crystals of ribonuclease from Streptomyces aureofaciens diffract to atomic resolution at room temperature. Using synchrotron radiation and an imaging-plate scanner, X-ray data have been recorded to 1.20 A resolution from a crystal of native enzyme and to 1.15 A from a crystal of a complex with guanosine-2'-monophosphate. Refinement with anisotropic atomic temperature factors resulted in increased accuracy of the structure. The R factors for the two structures are 10.6 and 10.9%. The estimated r.m.s. error in the coordinates is 0.05 A, less than half that obtained in the previous analysis at 1.7 A resolution. For the well ordered part of the main chain the error falls to below 0.02 A as estimated from inversion of the least-squares matrix. The two independent molecules in the asymmetric unit allowed detailed analysis of peptide planarity and some torsion angles. The high accuracy of the analysis revealed density for a partially occupied anion in the nucleotide binding site of molecule A in the native structure which was not seen at lower resolution. The anisotropic model allowed correction of the identity of the residue at position 72 from cysteine to threonine. Cys72 SG had been modelled in previous analyses with two conformations. The solvent structure was modelled by means of an automated procedure employing a set of objective criteria. The solvent structure for models refined using different programs with isotropic and anisotropic description of thermal motion is compared.
来自金色链霉菌的核糖核酸酶晶体在室温下可衍射至原子分辨率。利用同步辐射和成像板扫描仪，已从天然酶晶体记录到分辨率为1.20 Å的X射线数据，并从与2'-鸟苷单磷酸形成的复合物晶体记录到分辨率为1.15 Å的数据。采用各向异性原子温度因子进行精修提高了结构的准确性。这两种结构的R因子分别为10.6%和10.9%。坐标中的估计均方根误差为0.05 Å，不到之前在1.7 Å分辨率分析中获得值的一半。对于主链排列良好的部分，根据最小二乘矩阵求逆估计，误差降至0.02 Å以下。不对称单元中的两个独立分子使得能够对肽平面性和一些扭转角进行详细分析。分析的高精度揭示了天然结构中分子A核苷酸结合位点处部分占据阴离子的密度，这在较低分辨率下未观察到。各向异性模型允许将72位的残基身份从半胱氨酸校正为苏氨酸。在之前的分析中，Cys72 SG被模拟为两种构象。溶剂结构通过采用一组客观标准的自动化程序进行建模。比较了使用不同程序对热运动进行各向同性和各向异性描述所精修模型的溶剂结构。
