Choi K Y, Lu F, Zalkin H
Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907-1153.
J Biol Chem. 1994 Sep 30;269(39):24066-72.
The corepressor-binding domain of the Escherichia coli purine repressor (PurR) is homologous with several periplasmic sugar-binding proteins. Four amino acids in PurR were investigated for a role in binding of corepressors. Three of the residues, Asp146, Arg196 and Asp275, are conserved in periplasmic binding proteins for ribose, glucose/galactose, and arabinose and function to bind sugars. A fourth amino acid, Trp147, required for corepressor binding to PurR, corresponds to residues in glucose/galactose, ribose, and arabinose that also have a role in sugar binding. The four mutations that were constructed perturbed the binding of both hypoxanthine and guanine thus providing evidence for a single corepressor site/PurR subunit. The decreased corepressor binding affinity resulted in reduced affinity of mutant repressors for operator DNA in vitro and decreased capacity for repression in vivo. The corepressor-binding site in PurR appears to be similar to the conserved ligand-binding sites in the three periplasmic sugar-binding proteins and in the LacI family of repressors.
大肠杆菌嘌呤阻遏蛋白（PurR）的共阻遏物结合结构域与几种周质糖结合蛋白同源。研究了PurR中的四个氨基酸在共阻遏物结合中的作用。其中三个残基，即Asp146、Arg196和Asp275，在核糖、葡萄糖/半乳糖和阿拉伯糖的周质结合蛋白中保守，起到结合糖的作用。第四个氨基酸Trp147是共阻遏物与PurR结合所必需的，它对应于葡萄糖/半乳糖、核糖和阿拉伯糖中在糖结合中也起作用的残基。构建的四个突变干扰了次黄嘌呤和鸟嘌呤的结合，从而为单个共阻遏物位点/PurR亚基提供了证据。共阻遏物结合亲和力的降低导致突变阻遏物在体外对操纵子DNA的亲和力降低，以及在体内的阻遏能力下降。PurR中的共阻遏物结合位点似乎与三种周质糖结合蛋白和LacI家族阻遏物中的保守配体结合位点相似。
