Division of Chemistry and Chemical Engineering, Pasadena, California, USA.
Nat Struct Mol Biol. 2010 Mar;17(3):332-8. doi: 10.1038/nsmb.1770. Epub 2010 Feb 21.
ATP-binding cassette (ABC) transporters are integral membrane proteins that translocate a diverse array of substrates across cell membranes. We present here the dynamics of complex formation of three structurally characterized ABC transporters-the BtuCD vitamin B(12) importer and MetNI d/l-methionine importer from Escherichia coli and the Hi1470/1 metal-chelate importer from Haemophilus influenzae-in complex with their cognate binding proteins. Similarly to other ABC importers, MetNI interacts with its binding protein with low affinity (K(d) approximately 10(-4) M). In contrast, BtuCD-BtuF and Hi1470/1-Hi1472 form stable, high-affinity complexes (K(d) approximately 10(-13) and 10(-9) M, respectively). In BtuCD-BtuF, vitamin B(12) accelerates the complex dissociation rate approximately 10(7)-fold, with ATP having an additional destabilizing effect. The findings presented here highlight substantial mechanistic differences between BtuCD-BtuF, and likely Hi1470/1-Hi1472, and the better-characterized maltose and related ABC transport systems, indicating that there is considerable mechanistic diversity within this large protein super-family.
ATP 结合盒（ABC）转运蛋白是整合膜蛋白，可将各种底物跨细胞膜转运。我们在此介绍了三种结构特征明确的 ABC 转运蛋白 - 大肠杆菌的 BtuCD 维生素 B（12）进口器和 MetNI d/l-甲硫氨酸进口器以及流感嗜血杆菌的 Hi1470/1 金属螯合物进口器 - 与其同源结合蛋白形成复合物的动力学。与其他 ABC 进口器类似，MetNI 与结合蛋白的亲和力较低（K（d）约为 10（-4）M）。相比之下，BtuCD-BtuF 和 Hi1470/1-Hi1472 形成稳定的高亲和力复合物（K（d）分别约为 10（-13）和 10（-9）M）。在 BtuCD-BtuF 中，维生素 B（12）使复合物解离速率加速约 10（7）倍，ATP 具有额外的去稳定作用。这里介绍的发现强调了 BtuCD-BtuF 与更好表征的麦芽糖和相关 ABC 转运系统之间的实质性机制差异，表明在这个大型蛋白质超家族中存在相当大的机制多样性。
