Crystallization and preliminary X-ray diffraction studies of recombinant barley lectin and pro-barley lectin

Barley lectin (BL) and its precursor form (proBL), synthesized and over-expressed in Escherichia coli, have been crystallized under conditions identical to those used for the closely related lectin wheat germ agglutinin. These lectins are members of the Gramineae family and possess a unique disulfide-rich domain structure. The pro-lectin polypeptides are extended by 15 amino acid residues at the carboxy terminus. This pro-peptide, which is proteolytically removed as the mature lectin is deposited in the vacuoles, is thought to function as a targeting signal for molecular sorting. Crystals of BL and proBL are well ordered and belong to space groups C222(1) and P2(1)2(1)2(1). The unit cell dimensions for BL and proBL are a = 51.9 A, b = 73.7 A, c = 89.3 A (one monomer per asymmetric unit), and a = 45.2 A, b = 70.5 A, c = 111.6 A (two monomers per asymmetric unit), respectively. Diffraction patterns on precession photographs of BL crystals are closely similar to those of mature wheat germ agglutinin crystals, suggesting similar crystal packing and correct conformation of this recombinant protein in terms of the four structural domains and 16 disulfide bridges.