Mechanistically Novel Group of Membrane Transporters

ATP结合盒转运系统（ABC）在所有生命领域中形成了一个巨大的膜转运体群，它们在其中发挥着不同的作用，如营养摄取、蛋白质转运、离子稳态和耐药性。原核生物中所有先前已知的摄取ABC转运蛋白的一个特殊特征是存在细胞外底物结合蛋白。这些成分作为溶质受体和开关，刺激ATP水解和底物易位通过信号底物的可用性细胞质ABC域。在初步工作中，我们已经确定了数百名成员的一个新的组ABC摄取系统的金属和有机溶质，其机制不同于一般的概念在几个方面。这些转运蛋白含有ABC模块，并由ATP水解驱动。另一方面，它们在没有ABC模块的情况下显示基本活性，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，这些系统的详细的生物化学表征将揭示相关的功能，在一般的ABC型运输系统的机制的理解。

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.