Crystallization and preliminary x-ray analysis of the cytoplasmic domain of human erythrocyte band 3

A cytoplasmic domain of the human erythrocyte membrane protein band 3 (M(r) = 42,500), residues 1-379, expressed in and purified from E. coli, has been crystallized by the method of vapor diffusion in sitting drops with subsequent streak-seeding at room temperature. Initial crystals were grown from solutions containing 65-68% saturated ammonium sulfate at pH 4.9 and 2 mg/ml protein. Subsequent streak-seeding into solutions of 5053% ammonium sulfate at pH 4.9 and 7 mg/ml protein produced single crystals suitable for X-ray analysis, which contained pure protein as revealed by gel electrophoresis. The crystals belong to the monoclinic space group C2 with cell dimensions of a=178.8 Å, b=90.5 Å, c = 122.1 Å, and β = 131.3° and diffract at least to 2.7 Å resolution (at 100 K). A self-rotation function shows the presence of approximate 222 local symmetry.