Formation and dynamics of interacting electron transport chains

本文的目的是分析希瓦氏y型变形杆菌的质周和外膜跨越电子转移的基础。单胞菌是迄今为止在厌氧电子受体方面显示出最高灵活性的微生物，可用于呼吸。有趣的是，几乎所有的电子受体都在外周质或细胞表面被还原，电子向这些受体的转移依赖于c型细胞色素的活性。生物体进化出一个动态的电子传递网络，其中的电子传递链相互连接，同时产生。我们希望通过突变分析和伴随的细胞悬浮液中电子传递速率的测量以及快速动力学测量实验来了解该网络中电子传递的详细机制。此外，我们希望阐明外膜蛋白复合物形成的原理，使跨膜电子传递成为可能。该复合物由一个完整的β -桶蛋白（MtrB）组成，该蛋白连接了外质（MtrA）和细胞表面定位的c型细胞色素。有趣的是，我们可以证明在没有MtrA的情况下，MtrB会被周围质蛋白酶DegP降解，这表明MtrA是一种特殊的周围质伴侣，对于未折叠的β -桶蛋白通过周围质运输是必要的。此外，我们可以提供证据表明，膜中MtrB的折叠分别在MtrA存在和不存在时发生变化。通过体内和体外实验，我们旨在了解MtrA在MtrB形成和折叠中的详细功能。

It is the aim of this proposal to analyze the basis of periplasmic and outer membrane spanning electron transfer in the y-proteobacterium Shewanella oneidensis. S. oneidensis is so far the microorganism that shows the highest flexibility in terms of anaerobic electron acceptors, that can be used for respiration. Interestingly, almost all electron acceptors are reduced either in the periplasm or at the cell surface and the electron transfer to these acceptors is dependent on the activity of c-type cytochromes. A dynamic electron transfer network was evolved by the organism, in which the electron transfer chains are interconnected and produced simultaneously. We would like to understand the detailed mechanism of electron transport within this network via mutant analysis and concomitant measurement of electron transport rates in cell suspension and fast kinetic measurement experiments. Moreover, we would like to elucidate principles in the formation of an outer membrane protein complex that enables membrane spanning electron transport. The complex consists of an integral beta-barrel protein (MtrB) that connects a periplasmic (MtrA) and cell surface localized c-type cytochromes. Interestingly, we could show that MtrB is degraded by the periplasmic protease DegP in the absence of MtrA and it was suggested that MtrA is a specialized periplasmic chaperone that is necessary for transport of the unfolded beta-barrel protein through the periplasm. Furthermore, we could provide evidence that the fold of MtrB in the membrane varies in the presence and absence of MtrA, respectively. Via in vivo and in vitro experiments we aim to understand the detailed function of MtrA in formation and folding of MtrB.