Dautant A, Meyer J B, Yariv J, Précigoux G, Sweet R M, Kalb A J, Frolow F
Unité Biophysique Structurale, ERS133 CNRS, Université de Bordeaux 1, France.
Acta Crystallogr D Biol Crystallogr. 1998 Jan 1;54(Pt 1):16-24. doi: 10.1107/s0907444997006811.
Crystals of E. coli cytochrome b1, alias bacterioferritin, were grown fr om a low ionic strength solution. The resulting monoclniic P21 structure was solved by molecular replacement and refined using noncrystallographi c symmetries applied to the fundamental unit, consisting of two protein subunits and a single haem. From the Patterson self-rotation results it was shown that the asymmetric unit of the monoclinic crystal consists of 12 such dimers and corresponds to a complete, nearly spherical, molecule of bacterioferritin (M4 = 450 kDa) of 432 point-group symmetry. It is thus the most symmetrical cytochrome. As previously determined for the tetragonal form, the haem is located in a special position on a local twofold axis of the dimer. A bimetal centre is also observed within the four-helix bundle of each monomer; a metal-binding site is located on the fourfold axis.
大肠杆菌细胞色素b1（别名细菌铁蛋白）的晶体是从低离子强度溶液中生长出来的。通过分子置换解析出所得单斜晶系P21结构，并利用应用于基本单元的非晶体学对称性进行精修，该基本单元由两个蛋白质亚基和一个血红素组成。从帕特森自旋转结果表明，单斜晶体的不对称单元由12个这样的二聚体组成，对应于具有432点群对称性的完整、近乎球形的细菌铁蛋白分子（M4 = 450 kDa）。因此，它是最对称的细胞色素。如先前对四方晶系形式所确定的那样，血红素位于二聚体局部二重轴上的特殊位置。在每个单体的四螺旋束内也观察到一个双金属中心；一个金属结合位点位于四重轴上。
