Schumacher M A, Choi K Y, Zalkin H, Brennan R G
Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201-3098.
Science. 1994 Nov 4;266(5186):763-70. doi: 10.1126/science.7973627.
The three-dimensional structure of a ternary complex of the purine repressor, PurR, bound to both its corepressor, hypoxanthine, and the 16-base pair purF operator site has been solved at 2.7 A resolution by x-ray crystallography. The bipartite structure of PurR consists of an amino-terminal DNA-binding domain and a larger carboxyl-terminal corepressor binding and dimerization domain that is similar to that of the bacterial periplasmic binding proteins. The DNA-binding domain contains a helix-turn-helix motif that makes base-specific contacts in the major groove of the DNA. Base contacts are also made by residues of symmetry-related alpha helices, the "hinge" helices, which bind deeply in the minor groove. Critical to hinge helix-minor groove binding is the intercalation of the side chains of Leu54 and its symmetry-related mate, Leu54', into the central CpG-base pair step. These residues thereby act as "leucine levers" to pry open the minor groove and kink the purF operator by 45 degrees.
通过X射线晶体学以2.7埃的分辨率解析了嘌呤阻遏物PurR与它的辅阻遏物次黄嘌呤以及16碱基对的purF操纵基因位点形成的三元复合物的三维结构。PurR的二分结构由一个氨基末端DNA结合结构域和一个更大的羧基末端辅阻遏物结合及二聚化结构域组成，该羧基末端结构域与细菌周质结合蛋白的结构域相似。DNA结合结构域包含一个螺旋-转角-螺旋基序，它在DNA的大沟中形成碱基特异性接触。对称相关的α螺旋（“铰链”螺旋）的残基也与碱基接触，这些“铰链”螺旋深深结合在小沟中。铰链螺旋与小沟结合的关键是Leu54及其对称相关配对残基Leu54'的侧链插入中央的CpG碱基对步移中。这些残基因此充当“亮氨酸杠杆”，撬开小沟并使purF操纵基因扭结45度。
