Duda David, Govindasamy Lakshmanan, Agbandje-McKenna Mavis, Tu Chingkuang, Silverman David N, McKenna Robert
Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA.
Acta Crystallogr D Biol Crystallogr. 2003 Jan;59(Pt 1):93-104. doi: 10.1107/s0907444902019455. Epub 2002 Dec 19.
Using synchrotron radiation and a CCD detector, X-ray data have been collected at 100 K for the His64Ala mutant of human carbonic anhydrase II complexed with 4-methylimidazole (4-MI) to a maximal 1.05 A resolution, allowing full anisotropic least-squares refinement. The refined model has a conventional R factor of 15.7% for all reflections. The C(alpha) coordinates of the model presented here have an r.m.s. deviation of 0.10 A relative to the previously determined structure at 1.6 A resolution. Several amino-acid residues (six of the 255 observed) have been identified with multiple rotamer side-chain conformations. C, N and O atoms can be differentiated with selective electron-density map contouring. The estimated standard deviations for all main-chain non-H atom bond lengths and angles are 0.013 and 0.030 A, respectively, based on unrestrained full-matrix least-squares refinement. This structure gives detailed information about the tetrahedrally arranged zinc ion coordinated by three histidine N atoms (His94 N(epsilon 2), His96 N(epsilon2) and His119 N(delta1)) and a water/hydroxide, the multiple binding sites of the proton chemical rescue molecule 4-MI and the solvent networks linking the zinc-bound water/hydroxide and 4-MI molecules. This structure presents the highest resolution structure of a carbonic anhydrase isozyme so far determined and adds to the understanding of proton-transfer processes.
利用同步辐射和电荷耦合器件（CCD）探测器，在100 K下收集了与4-甲基咪唑（4-MI）复合的人碳酸酐酶II的His64Ala突变体的X射线数据，分辨率最高达到1.05 Å，从而可以进行完全各向异性最小二乘法精修。精修后的模型对所有反射的传统R因子为15.7%。本文给出的模型的Cα坐标相对于之前在1.6 Å分辨率下确定的结构，均方根偏差为0.10 Å。已鉴定出几个氨基酸残基（在观察到的255个残基中有6个）具有多个旋转异构体侧链构象。通过选择性电子密度图等高线可以区分C、N和O原子。基于无约束全矩阵最小二乘法精修，所有主链非氢原子键长和键角的估计标准偏差分别为0.013 Å和0.030 Å。该结构给出了由三个组氨酸N原子（His94 N(ε2)、His96 N(ε2)和His119 N(δ1)）和一个水/氢氧根配位的四面体排列锌离子的详细信息、质子化学救援分子4-MI的多个结合位点以及连接锌结合水/氢氧根和4-MI分子的溶剂网络。该结构是目前已确定的碳酸酐酶同工酶的最高分辨率结构，有助于增进对质子转移过程的理解。
