Purification, solution properties and crystallization of SIV integrase containing a continuous core and C-terminal domain

The C-terminal two-thirds segment of integrase derived from the simian immu nodeficiency virus has been cloned, expressed in Escherichia coli, and puri fied to greater than 95% homogeneity. The protein encompasses amino-acid re sidues 50-293 and contains a F185H substitution to enhance solubility. In d ilute solutions at concentrations below 1 mg ml(-1), the enzyme is predomin antly dimeric. At the higher concentrations (>10 mg ml(-1)) required to ena ble crystallization, the enzyme self-associates to form species with molecu lar weights greater than 200 kDa. Despite the apparent high aggregation in solution, the enzyme crystallizes from a 8%(v/v) polyethylene glycol (molec ular weight 6000) solution in a form suitable for X-ray diffraction studies . The resulting single crystals belong to the space group P2(1)2(1)2(1), wi th unit-cell parameters a = 79.76, b = 99.98, c = 150.2 Angstrom, alpha = b eta = gamma = 90 degrees and Z = 4. Under X-ray irradiation generated with a rotating-anode generator, the crystals diffract to 2.8 Angstrom resolutio n and allow collection of a native 3 Angstrom resolution diffraction data s et.