Crystal structure and reaction mechanism of urate oxidase from Bacillus sp.

以2.2A的分辨率测定了芽孢杆菌（Bacillus Sp., bUOX）尿酸氧化酶的晶体结构。利用Mar CCD相机和同步辐射在BL41XU （Spring-8, Harima, Japan）束流线上采集了晶体的x射线衍射数据。晶体属于P2_12_12空间群，单位胞参数a=133.5, b=144.5, c=78.8A。利用分子置换技术对uox -8-叠氮黄嘌呤配合物的结构进行了解析。我们的初始模型采用来自黄曲霉（Asperigillus flavus）的UOX （PDS编码1UOX； Colloc'h et al.(1997)）的精化结构，其残基全部用丙氨酸代替。使用Refmac5 （CCP4 Project No.4(1999)）进行的约束细化导致数据的r值为22% （PDB代码：1J2G）。四尺度界面环的主链结构与黄曲霉UOX有显著差异。随着盐浓度的变化，UOX晶体质量的不稳定性阻碍了Xe衍生物的制备。然而，盐对bUOX的另一个影响是其热稳定性随盐浓度的增加而增加。有趣的是，四聚体界面上的一个环含有R298，硫酸盐离子似乎连接了与非晶体双重对称相关的亚基。

Crystal structure of urate oxidase from Bacillus Sp. (bUOX) has been determined at 2.2A resolution. X-Ray diffraction data for the crystals were collected using a Mar CCD camera and synchrotron radition on beam line BL41XU (Spring-8, Harima, Japan). The crystals belong to space group P2_12_12 with unitcell parameters a=133.5, b=144.5, c=78.8A.The structure of UOX-8-azaxanthine complex has been solved by molecular replacement techniques. The refined structure of UOX from Asperigillus flavus (PDS code 1UOX; Colloc'h et al. (1997)) was used as our initial model, all the residues of which were replaced with alanines. Restrained refinement with Refmac5 (CCP4 Project No.4 (1999)) resulted in an R-value of 22% for the data (PDB code: 1J2G). Main chain structures of the loops at tetrametric interface are significantly different from those of A. flavus UOX.Instability of the b UOX crystal quality in changing salt concentration prevents from preparing Xe derivatives. However, another salt effect to bUOX was found that its thermal stability increases with salt concentration. Interestingly, one of the loops at the tetrameric interface contains R298 and a sulfate ion seems to bridge the subunits related with a non-crystallographic two-fold sysmmetry.