X-ray analysis of crystals of rat phosphatidylinositol-transfer protein with bound phosphatidylcholine

Phosphatidylinositol-transfer protein (PITP) is a soluble, ubiquitously expressed, highly conserved protein encoded by two genes in humans, rodents and other mammals. A cDNA encoding the alpha isoform of the rat gene was expressed to high levels in Escherichia coli, the protein purified and the homogeneous protein used for crystallization studies. Crystals of rat PITP-alpha were obtained by vapor-diffusion techniques using the sitting-drop method. Crystals grow within two weeks by vapor-diffusion techniques in the presence of polyethylene glycol 4000. Both crystal forms pack in the monoclinic space group P21. Crystal form I has unit-cell parameters a = 44.75, b = 74.25, c = 48.32 A and beta = 114.14 degrees. Unit-cell parameters for crystal form II are a = 47.86, b = 73.59, c = 80.49 A and beta = 98.54 degrees. Crystal form I has a Vm of 2.295 A3 Da-1 and an estimated solvent content of 46.4% with one molecule per asymmetric unit, while crystal form II has a Vm of 2.196 A3 Da-1 and an estimated solvent content of 44.0%, assuming two molecules per asymmetric unit.