Hars U, Horlacher R, Boos W, Welte W, Diederichs K
Department of Biology, University of Konstanz, Germany.
Protein Sci. 1998 Dec;7(12):2511-21. doi: 10.1002/pro.5560071204.
The crystal structure of the Escherichia coli trehalose repressor (TreR) in a complex with its inducer trehalose-6-phosphate was determined by the method of multiple isomorphous replacement (MIR) at 2.5 A resolution, followed by the structure determination of TreR in a complex with its noninducer trehalose at 3.1 A resolution. The model consists of residues 61 to 315 comprising the effector binding domain, which forms a dimer as in other members of the LacI family. This domain is composed of two similar subdomains each consisting of a central beta-sheet sandwiched between alpha-helices. The effector binding pocket is at the interface of these subdomains. In spite of different physiological functions, the crystal structures of the two complexes of TreR turned out to be virtually identical to each other with the conformation being similar to those of the effector binding domains of the LacI and PurR in complex with their effector molecules. According to the crystal structure, the noninducer trehalose binds to a similar site as the trehalose portion of trehalose-6-phosphate. The binding affinity for the former is lower than for the latter. The noninducer trehalose thus binds competitively to the repressor. Unlike the phosphorylated inducer molecule, it is incapable of blocking the binding of the repressor headpiece to its operator DNA. The ratio of the concentrations of trehalose-6-phosphate and trehalose thus is used to switch between the two alternative metabolic uses of trehalose as an osmoprotectant and as a carbon source.
通过多同晶置换法（MIR）在2.5埃分辨率下测定了大肠杆菌海藻糖阻遏物（TreR）与其诱导剂6-磷酸海藻糖复合物的晶体结构，随后在3.1埃分辨率下测定了TreR与其非诱导剂海藻糖复合物的晶体结构。该模型由61至315位残基组成，包含效应物结合结构域，该结构域如LacI家族的其他成员一样形成二聚体。该结构域由两个相似的亚结构域组成，每个亚结构域由夹在α-螺旋之间的中央β-折叠组成。效应物结合口袋位于这些亚结构域的界面处。尽管生理功能不同，但TreR的两种复合物的晶体结构彼此几乎相同，其构象与LacI和PurR与其效应物分子复合物的效应物结合结构域的构象相似。根据晶体结构，非诱导剂海藻糖与6-磷酸海藻糖的海藻糖部分结合到相似的位点。前者的结合亲和力低于后者。因此，非诱导剂海藻糖竞争性地与阻遏物结合。与磷酸化的诱导剂分子不同，它不能阻止阻遏物头部与操纵子DNA的结合。因此，6-磷酸海藻糖和海藻糖浓度的比例用于在海藻糖作为渗透保护剂和碳源的两种替代代谢用途之间进行切换。
