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

Phosphatidylinositol-transfer protein (PITP) is a soluble, ubiquitously exp ressed, highly conserved protein encoded by two genes in humans, rodents an d other mammals. A cDNA encoding the alpha isoform of the rat gene was expr essed to high levels in Escherichia coli, the protein purified and the homo geneous protein used for crystallization studies. Crystals of rat PITP-alph a were obtained by vapor-diffusion techniques using the sitting-drop method . Crystals grow within two weeks by vapor-diffusion techniques in the prese nce of polyethylene glycol 4000. Both crystal forms pack in the monoclinic space group PZ,. Crystal form I has unit-cell parameters a = 44.75, b = 74. 25, c = 48.32 Angstrom and beta = 114.14 degrees. Unit-cell parameters for crystal form II are a = 47.86, b = 73.59, c = 80.49 Angstrom and beta = 98. 54 degrees. Crystal form I has a V-m of 2.295 Angstrom(3) Da(-1) and an est imated solvent content of 46.4% with one molecule per asymmetric unit, whil e crystal form II has a V-m of 2.196 Angstrom(3) Da(-1) and an estimated so lvent content of 44.0%, assuming two molecules per asymmetric unit.