Purification and crystallization of the respiratory complex formate dehydrogenase-N from Escherichia coli

A membrane-protein complex, formate dehydrogenase-N from Escherichia coli, has been purified and crystallized. This molybdenum-containing enzyme, composed of α, β and γ subunits, is the major electron donor to the nitrate respiratory chain of E. coli. The formate dehydrogenase-N crystals belong to the cubic space group P2₁3, with unit-cell parameters a = b = c = 203 Å. An asymmetric unit of the crystals is assumed to contain one formate dehydrogenase-N monomer (MW 170 kDa). One data set to 1.6 Å resolution, with 342 711 independent observations (94.4% complete) and an R_merge of 0.08, has been collected from a single crystal. This is the highest resolution data set reported for a membrane-protein complex to date.