Crystallization of the Membrane-Associated Annexin B1: Roles of Additive Screen, Dynamic Light Scattering, and Bioactivity Assay

Annexin B1 (AnxB1) is a calcium-dependent phospholipid binding protein from Taenia solium cysticercus and has been reported to possess anticoagulant activity, to inhibit phospholipase A 2, and to regulate membrane transport. Native AnxB1 and its selenomethionyl derivative have been overproduced in Escherichia coli and purified. The results of dynamic light scattering analysis showed that Hepes buffer combined with low concentration salts (NaCl or CaCl 2 ) was beneficial for preventing aggregation and for AnxB1 stabilization in the storage. After the additive screen, crystals have been yielded in the presence of guanidine hydrochloride (Gn-HCl). We determined that a low concentration of Gn-HCl significantly delayed clotting time and increased anticoagulant activity. Analysis of the crystal showed that in the presence of Gn-HCl, AnxB1 crystallizes in orthorhombic space group, which is modified from the cubic space group for crystals grown in the absence of Gn-HCl. A high quality data set (at 1.9 Å) has been collected successfully for crystals of l -selenomethionine labeled protein in the presence of Gn-HCl, to solve the structure with the single anomalous dispersion method (SAD). The unit cell parameters are a = 102.35 Å, b = 103.59 Å, c = 114.60 Å, α = β = γ = 90.00°.