Törnroth Susanna, Yankovskaya Victoria, Cecchini Gary, Iwata So
Department of Biochemistry, Uppsala University, Sweden.
Biochim Biophys Acta. 2002 Jan 17;1553(1-2):171-6. doi: 10.1016/s0005-2728(01)00236-5.
A membrane protein complex, succinate dehydrogenase (SQR) from Escherichia coli has been purified and crystallised. This enzyme is composed of four subunits containing FAD, three iron-sulphur clusters and one haem b as prosthetic groups. The obtained crystals belong to the hexagonal space group P6(3) with the unit-cell dimensions of a=b=123.8 A and c=214.6 A. An asymmetric unit of the crystals contains one SQR monomer (M(r) 120 kDa). A data set is now available at 4.0 A resolution with 88.1% completeness and 0.106 R(merge). We have obtained a molecular replacement solution that shows sensible molecular packing, using the soluble domain of E. coli QFR (fumarate reductase) as a search model. The packing suggests that E. coli SQR is a crystallographic trimer rather than a dimer as observed for the E. coli QFR.
一种膜蛋白复合物，来自大肠杆菌的琥珀酸脱氢酶（SQR）已被纯化并结晶。这种酶由四个亚基组成，含有FAD、三个铁硫簇和一个血红素b作为辅基。获得的晶体属于六方空间群P6(3)，晶胞参数为a = b = 123.8 Å，c = 214.6 Å。晶体的一个不对称单元包含一个SQR单体（分子量120 kDa）。现在有一个分辨率为4.0 Å的数据集，完整性为88.1%，合并R因子为0.106。我们使用大肠杆菌QFR（延胡索酸还原酶）的可溶性结构域作为搜索模型，获得了一个显示合理分子堆积的分子置换解。这种堆积表明大肠杆菌SQR是一个晶体学三聚体，而不像大肠杆菌QFR那样是二聚体。
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