Purification, crystallisation and preliminary crystallographic studies of succinate:ubiquinone oxidoreductase from Escherichia coli

摘要

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.