Oswald Christine, Smits Sander H J, Höing Marina, Bremer Erhard, Schmitt Lutz
Institute of Biochemistry, Heinrich Heine University Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany.
Biol Chem. 2009 Nov;390(11):1163-70. doi: 10.1515/BC.2009.113.
The periplasmic ligand-binding protein ChoX is part of the ABC transport system ChoVWX that imports choline as a nutrient into the soil bacterium Sinorhizobium meliloti. We have recently reported the crystal structures of ChoX in complex with its ligands choline and acetylcholine and the structure of a fully closed but substrate-free state of ChoX. This latter structure revealed an architecture of the ligand-binding site that is superimposable to the closed, ligand-bound form of ChoX. We report here the crystal structure of ChoX in an unusual, ligand-free conformation that represents a semi-closed form of ChoX. The analysis revealed a subdomain movement in the N-lobe of ChoX. Comparison with the two well-characterized substrate binding proteins, MBP and HisJ, suggests the presence of a similar subdomain in these proteins.
周质配体结合蛋白ChoX是ABC转运系统ChoVWX的一部分，该系统将胆碱作为营养物质导入土壤细菌苜蓿中华根瘤菌。我们最近报道了与配体胆碱和乙酰胆碱结合的ChoX的晶体结构以及ChoX完全封闭但无底物状态的结构。后一种结构揭示了配体结合位点的结构，该结构与ChoX的封闭、配体结合形式重叠。我们在此报告ChoX处于一种不寻常的无配体构象的晶体结构，该构象代表ChoX的半封闭形式。分析揭示了ChoX N叶中的一个亚结构域运动。与两种特征明确的底物结合蛋白MBP和HisJ的比较表明，这些蛋白中存在类似的亚结构域。
