Crystallization and preliminary X-ray diffraction analysis of the 16-haem cytochrome of Desulfovibrio gigas

High-molecular-weight cytochromes (Hmcs) belong to a large family of multihaem cytochromes in sulfate-reducing bacteria. HmcA is the first cytochrome reported to have 16 c-type haems arranged in its polypeptide chain. The function of this cytochrome is still unknown, although it is clear that it belongs to a membrane-bound complex involved in electron transfer from the periplasm to the membrane. HmcA from Desulfovibrio gigas has been purified and successfully crystallized using the hanging-drop vapour-diffusion method. The crystals grew using PEG and zinc acetate as precipitants to maximum dimensions of 0.2 × 0.2 × 0.2 mm in an orthorhombic space group, with unit-cell parameters a = 88.9, b = 90.9, c = 83.7 Å. The crystals diffracted to beyond 2.07 Å and a MAD data set was collected.