Purification, crystallization and preliminary crystallographic analysis of a natural complex of phospholipase A₂ from Echis carinatus (saw-scaled viper)

A novel complex of phospholipase A₂ complexed with another venom protein has been isolated and purified from saw-scaled viper (Echis carinatus) venom. The molecular weights of the two components are 16 and 14 kDa, respectively. The complex was purified using an Affigel blue column and an anion-exchange (DEAE Sephacel) column. Long diamond-shaped crystals were obtained by hanging-drop vapour diffusion. The protein complex was dissolved at a concentration of 10 mg ml⁻¹ in 20 mM sodium cacodylate, 1 mM CaCl₂ and 2% dioxane at pH 6.0. The reservoir contained the same buffer with 7%(w/v) PEG 4000. Crystals appeared within 2–3 weeks. Native data to 2.9 Å resolution have been obtained at 291 K. The crystals belong to the monoclinic space group P2₁ with unit-cell parameters a = 74.47, b = 47.87, c = 106.39 Å, β = 104.5° and contain two molecules per asymmetric unit. Structure determination by molecular replacement is in progress.