Crystallization of chicken egg white lysozyme from assorted sulfate salts

Chicken egg white lysozyme has been found to crystallize from ammonium, sodium, potassium, rubidium, magnesium, and manganese sulfates at acidic and basic pH, with protein concentrations from 60 to 190 mg/ml. Crystals have also been grown at 4°C in the absence of any other added salts using isoionic lysozyme which was titrated to pH 4.6 with dilute sulfuric acid. Four different crystal forms have been obtained, depending upon the temperature, protein concentration, and precipitating salt employed. Crystals grown at 15°C were generally tetragonal, with space group P4₃2₁2. Crystallization at 20°C typically resulted in the formation of orthorhombic crystals, space group P2₁2₁2₁. The tetragonal ↔ orthorhombic transition appeared to be a function of both the temperature and protein concentration, occurring between 15 and 20°C and between 100 and 125 mg/ml protein concentration. Crystallization from 1.2 M magnesium sulfate at pH 7.8 gave a trigonal crystal, space group P3₁2₁, a = b = 87.4, c = 73.7, γ = 120°, which diffracted to 2.8 Å. Crystallization from ammonium sulfate at pH 4.6, generally at lower temperatures, was also found to result in a monoclinic form, space group C2, a = 65.6, b = 95.0, c = 41.2, β= 119.2°. A crystal of ∼0.2 × 0.2 × 0.5 mm grown from bulk solution diffracted to ∼3.5 Å.