Haupt Melina, Bramkamp Marc, Coles Murray, Altendorf Karlheinz, Kessler Horst
Institut für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany.
J Mol Biol. 2004 Oct 1;342(5):1547-58. doi: 10.1016/j.jmb.2004.07.060.
P-type ATPases are involved in the active transport of ions across biological membranes. The KdpFABC complex (P-type ATPase) of Escherichia coli is a high-affinity K+ uptake system that operates only when the cell experiences osmotic stress or K+ limitation. Here, we present the solution structure of the nucleotide binding domain of KdpB (backbone RMSD 0.17 A) and a model of the AMP-PNP binding mode based on intermolecular distance restraints. The calculated AMP-PNP binding mode shows the purine ring of the nucleotide to be "clipped" into the binding pocket via a pi-pi-interaction to F377 on one side and a cation-pi-interaction to K395 on the other. This binding mechanism seems to be conserved in all P-type ATPases, except the heavy metal transporting ATPases (type IB). Thus, we conclude that the Kdp-ATPase (currently type IA) is misgrouped and has more similarities to type III ATPases. The KdpB N-domain is the smallest and simplest known for a P-type ATPase, and represents a minimal example of this functional unit. No evidence of significant conformational changes was observed within the N-domain upon nucleotide binding, thus ruling out a role for ATP-induced conformational changes in the reaction cycle.
P型ATP酶参与离子跨生物膜的主动运输。大肠杆菌的KdpFABC复合体（P型ATP酶）是一种高亲和力的钾离子摄取系统，仅在细胞经历渗透胁迫或钾离子限制时起作用。在此，我们展示了KdpB核苷酸结合结构域的溶液结构（主链均方根偏差为0.17 Å）以及基于分子间距离约束的AMP-PNP结合模式模型。计算得出的AMP-PNP结合模式显示，核苷酸的嘌呤环通过一侧与F377的π-π相互作用以及另一侧与K395的阳离子-π相互作用“夹入”结合口袋。除重金属转运ATP酶（IB型）外，这种结合机制似乎在所有P型ATP酶中都是保守的。因此，我们得出结论，Kdp-ATP酶（目前为IA型）分类错误，与III型ATP酶有更多相似之处。KdpB的N结构域是已知的P型ATP酶中最小且最简单的，代表了该功能单元的一个最小实例。在核苷酸结合时，未观察到N结构域内有明显的构象变化，因此排除了ATP诱导的构象变化在反应循环中的作用。
