3.3. Protein Crystallization

XopAI crystals were grown via the hanging-drop vapor-diffusion method at room temperature. The P4₃2₁2 crystals of full-length XopAI were grown by mixing 1 μL of protein solution with 1 μL of a crystallization buffer containing 15% (v/v) PEG 400, 5.5% (w/v) PEG 20000, and 50 mM KH₂PO₄, pH 8.0. The P4₁2₁2 crystals of full-length XopAI were grown by mixing 1 μL of protein solution with 1 μL of 10 mM β-mercaptoethanol and 1 μL of crystallization buffer. The buffer is similar to that for the P4₃2₁2 crystals, and it consists of 16.5% (v/v) PEG 400, 6.5% (w/v) PEG 20000, and 50 mM KH₂PO₄, pH 8.0. The crystals of XopAI-ΔN70 were grown by mixing 2 μL of protein solution and 1 μL of crystallization buffer containing 10% (v/v) 2-propanol, 20% (w/v) PEG400, and 100 mM HEPES-NaOH, pH 9.5.