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 immunodeficiency virus has been cloned, expressed in Escherichia coli, and purified to greater than 95% homogeneity. The protein encompasses amino-acid residues 50–293 and contains a F185H substitution to enhance solubility. In dilute solutions at concentrations below 1 mg ml−1, the enzyme is predominantly dimeric. At the higher concentrations (>10 mg ml−1) required to enable crystallization, the enzyme self-associates to form species with molecular weights greater than 200 kDa. Despite the apparent high aggregation in solution, the enzyme crystallizes from a 8%(v/v) polyethylene glycol (molecular weight 6000) solution in a form suitable for X-ray diffraction studies. The resulting single crystals belong to the space group P212121, with unit-cell parameters a = 79.76, b = 99.98, c = 150.2 A, α = β = γ = 90° and Z = 4. Under X-ray irradiation generated with a rotating-anode generator, the crystals diffract to 2.8 A resolution and allow collection of a native 3 A resolution diffraction data set.