Mechanistically Novel Group of Membrane Transporters

含ATP结合盒的转运系统(ABC)在所有生命王国中形成一个庞大的膜转运体，它们在其中扮演着不同的角色，如营养吸收、蛋白质转运、离子动态平衡和耐药性。所有已知的原核生物摄取ABC转运蛋白的一个特殊特征是存在胞外底物结合蛋白。这些组分作为溶质受体和开关，通过向细胞质ABC结构域发送底物可获得性信号来刺激ATP水解和底物转运。在初步工作中，我们鉴定了一组新的ABC金属和有机溶质摄取系统的数百个成员，其机制在几个方面与一般概念不同。这些转运蛋白含有ABC模块，由ATP水解酶驱动。另一方面，它们在没有ABC模块的情况下表现出基本的活性，并且这两种活性都不依赖于细胞外溶质结合蛋白。我们相信，对这些系统的详细生化特征将揭示出与理解ABC类型运输系统的机制有关的一般特征。

ATP-binding cassette-containing (ABC) transport systems form a huge group of membrane transporters in all kingdoms of life in which they play diverse roles such as nutrient uptake, protein translocation, ion homeostasis, and drug resistance. A special feature of all previously known uptake ABC transporters in prokaryotes is the existence of extracellular substrate-binding proteins. These components act as solute receptors and as switches that stimulate ATP hydrolysis and substrate translocation through signalling substrate availability to the cytoplasmic ABC domains. In preliminary work, we have identified several hundred members of a novel group of ABC uptake systems for metals and organic solutes, the mechanism of which differs from the general concept in several respects. These transporters contain ABC modules and are driven by ATP hydrolysis. On the other hand, they display a basic activity in the absence of an ABC module and both activities are independent of extracellular solute-binding proteins. We are convinced that a detailed biochemical characterization of these systems will uncover features that are relevant in general for an understanding of the mechanism of ABC-type transport systems.