1.7.2.3 hanging drop vapor diffusion method 1.7.2.3 recombinant monomeric, dimeric, and trimeric forms, hanging drop vapour diffusion method, 4°C, 0.001 ml of 1.2 mg/ml protein in 20 mM Tris-HCl, pH 8.0, 220 mM NaCl, 10 mM DTT, mixed with equal volume of reservoir solution containing 1.6 M ammonium sulfate, 100 mM MES, pH 6.4, 4-6 days, cryoprotection by addition of 15% w/v ethylene glycerol to the reservoir solution, X-ray diffraction structure determination and analysis at 2.42 A resolution