Wright C S, Schroeder M R, Raikhel N V
Department of Biochemistry and Molecular Biophysics, Virginia Commonwealth University, Richmond 23298.
J Mol Biol. 1993 Sep 20;233(2):322-4. doi: 10.1006/jmbi.1993.1511.
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.
大麦凝集素（BL）及其前体形式（proBL）在大肠杆菌中合成并过量表达，已在与密切相关的凝集素麦胚凝集素相同的条件下结晶。这些凝集素是禾本科家族的成员，具有独特的富含二硫键的结构域结构。前凝集素多肽在羧基末端延伸了15个氨基酸残基。这种前肽在成熟凝集素沉积在液泡中时被蛋白水解去除，被认为作为分子分选的靶向信号发挥作用。BL和proBL的晶体排列良好，分别属于空间群C222(1)和P2(1)2(1)2(1)。BL的晶胞尺寸为a = 51.9 Å，b = 73.7 Å，c = 89.3 Å（每个不对称单元一个单体），proBL的晶胞尺寸为a = 45.2 Å，b = 70.5 Å，c = 111.6 Å（每个不对称单元两个单体）。BL晶体的进动照片上的衍射图案与成熟麦胚凝集素晶体的衍射图案非常相似，表明就四个结构域和16个二硫键而言，该重组蛋白具有相似的晶体堆积和正确的构象。
