The K+-translocating KdpFABC complex from Escherichia coli:: A p-type ATPase with unique features
The K+-translocating KdpFABC complex from Escherichia coli:: A p-type ATPase with unique features
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DOI：
10.1007/s10863-007-9111-0
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发表时间：
2007-12-01
影响因子：
3
通讯作者：
Altendorf, Karlheinz
中科院分区：
文献类型：
--
作者：
Greie, Joerg-Christian;Altendorf, Karlheinz
来自肠杆菌大肠杆菌的原核 KdpFABC 复合物代表了一种独特类型的 P 型 ATP 酶，由四个不同的亚基组成，其中具有催化活性的 P 型 ATP 酶在进化中招募了钾通道模块，以促进 ATP 驱动的钾在陡峭的浓度梯度下转运到细菌细胞中。这种不寻常的组成需要相对于其他 P 型 ATP 酶的特殊特征，例如，这种多亚基酶复合物中两种不同多肽上的 ATP 水解和底物转运位点的空间分离，这反过来又导致了有趣的偶联机制。与所有其他 P 型 ATP 酶一样，KdpFABC 复合物在催化过程中也在所谓的 E1 和 E2 状态之间循环，每种状态都包含不同的结构特性以及对 ATP 和转运底物的不同结合亲和力。最近在工作酶中观察到了这种运输循环的独特结构。 P 型 ATP 酶的所有典型特征均归因于 KdpB 亚基，该亚基还与其他 P 型 ATP 酶家族成员具有很强的结构同源性。然而，转运底物钾的易位是由 KdpA 亚基介导的，该亚基与 MPM 型钾通道（例如来自浅青紫链霉菌的 KcsA）具有结构和功能同源性。长期以来，KdpC 亚基一直被认为在 KdpFABC 活性的调节中表现出类似 FXYD 蛋白的功能。然而，我们的最新结果支持这样的观点，即 KdpC 可能充当催化伴侣，它与待水解的核苷酸相互作用，从而增加 KdpB 核苷酸结合域的相当不典型的弱核苷酸结合亲和力。
The prokaryotic KdpFABC complex from the enterobacterium Escherichia coli represents a unique type of P-type ATPase composed of four different subunits, in which a catalytically active P-type ATPase has evolutionary recruited a potassium channel module in order to facilitate ATP-driven potassium transport into the bacterial cell against steep concentration gradients. This unusual composition entails special features with respect to other P-type ATPases, for example the spatial separation of the sites of ATP hydrolysis and substrate transport on two different polypeptides within this multisubunit enzyme complex, which, in turn, leads to an interesting coupling mechanism. As all other P-type ATPases, also the KdpFABC complex cycles between the so-called E1 and E2 states during catalysis, each of which comprises different structural properties together with different binding affinities for both ATP and the transport substrate. Distinct configurations of this transport cycle have recently been visualized in the working enzyme. All typical features of P-type ATPases are attributed to the KdpB subunit, which also comprises strong structural homologies to other P-type ATPase family members. However, the translocation of the transport substrate, potassium, is mediated by the KdpA subunit, which comprises structural as well as functional homologies to MPM-type potassium channels like KcsA from Streptomyces lividans. Subunit KdpC has long been thought to exhibit an FXYD protein-like function in the regulation of KdpFABC activity. However, our latest results are in favor of the notion that KdpC might act as a catalytical chaperone, which cooperatively interacts with the nucleotide to be hydrolyzed and, thus, increases the rather untypical weak nucleotide binding affinity of the KdpB nucleotide binding domain.