Structure and mechanism of a group-I cobalt energy coupling factor transporter
Structure and mechanism of a group-I cobalt energy coupling factor transporter
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I族钴能量耦合因子转运体的结构与机制
DOI：
10.1038/cr.2017.38
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发表时间：
2017-05-01
期刊：
影响因子：
44.1
通讯作者：
Zhang, Peng
中科院分区：
文献类型：
--
作者：
Bao, Zhihao;Qi, Xiaofeng;Zhang, Peng
能量偶联因子(ECF)转运蛋白是近年来在微生物中发现的一大类ATP结合盒转运蛋白。ECF转运体负责从环境中摄取微量营养素，是由膜底物结合组件ECFS和ECF模块组成的模块化转运体，ECF组件由完整的膜支架组件ECfT和两个细胞质ATP结合/水解组分ECFA/A‘组成。ECF转运蛋白分为I类和II类。目前，对I类ECF转运蛋白的分子理解非常有限，部分原因是缺乏转运蛋白复杂的结构信息。在这里，我们介绍了第I族钴ECF转运体CbiMNQO的结构和基于结构的分析，其组成的亚基CBIM/CbiN、CbiQ和CbiO分别对应于第II族ECF转运体的ECFS、ECFT和ECFA组分。通过CbiMNQO不同亚基的重组以及相关ATPase和转运蛋白活性的测定，发现底物结合亚基CBIM能够刺激CbiQO的基础ATPase活性。CbiMQO络合物的结构确定为向内开放构象，CbiO的结构确定为β，γ-亚甲基腺苷5‘-三磷酸结合的闭合构象。基于结构的分析揭示了不同组分之间的相互作用，CBIM L1环的底物门控功能，以及由ATP结合和CbiMNQO转运蛋白复合体内的产物释放引起的CbiO的构象变化。这些发现使我们能够提出一个CbiMNQO转运蛋白的工作模型，在该模型中，转运过程需要CbiQ和CBIM的旋转或倾覆，而CbiN可能在CbiQ和CBIM之间的构象变化耦合中发挥作用。
Energy-coupling factor (ECF) transporters are a large family of ATP-binding cassette transporters recently identified in microorganisms. Responsible for micronutrient uptake from the environment, ECF transporters are modular transporters composed of a membrane substrate-binding component EcfS and an ECF module consisting of an integral membrane scaffold component EcfT and two cytoplasmic ATP binding/hydrolysis components EcfA/A'. ECF transporters are classified into groups I and II. Currently, the molecular understanding of group-I ECF transporters is very limited, partly due to a lack of transporter complex structural information. Here, we present structures and structure-based analyses of the group-I cobalt ECF transporter CbiMNQO, whose constituting subunits CbiM/CbiN, CbiQ, and CbiO correspond to the EcfS, EcfT, and EcfA components of group-II ECF transporters, respectively. Through reconstitution of different CbiMNQO subunits and determination of related ATPase and transporter activities, the substrate-binding subunit CbiM was found to stimulate CbiQO's basal ATPase activity. The structure of CbiMQO complex was determined in its inward-open conformation and that of CbiO in β, γ-methyleneadenosine 5′-triphosphate-bound closed conformation. Structure-based analyses revealed interactions between different components, substrate-gating function of the L1 loop of CbiM, and conformational changes of CbiO induced by ATP binding and product release within the CbiMNQO transporter complex. These findings enabled us to propose a working model of the CbiMNQO transporter, in which the transport process requires the rotation or toppling of both CbiQ and CbiM, and CbiN might function in coupling conformational changes between CbiQ and CbiM.