Control of membrane dynamics by cooperative action of bacterial dynamin-like proteins and flotillins

蛋白质和脂质在生物膜上分布不均。膜蛋白的正确功能往往依赖于在确定的膜区域内的时空组织。然而，细菌细胞膜的横向组织尚未被详细分析，其对细胞质分裂和发育等细胞过程的影响在很大程度上仍然未知。我们已经确定了一种细菌漂浮体，它存在于膜微域中，可能有助于侧膜组织。Flotillins是筏子标记蛋白，在翻译后水平被广泛修饰。这些蛋白质组装成寡聚复合物，可能调节它们的功能。利用各向异性染料laudan，我们已经能够证明细菌浮胞直接影响膜的有序，可能是通过阻止液体有序区域的聚结。我们将分析枯草芽孢杆菌中的细菌浮胞素同源物如何能够介导空间膜组织，以及这如何影响膜整体蛋白机制（如分泌系统）的功能。此外，我们还发现了一种细菌动力蛋白样蛋白，DynA以核苷酸独立的方式与带负电荷的磷脂结合。DynA参与了膜系结和融合。DynA定位于鼻中隔，可能有助于有效的鼻中隔闭合。DynA在膜表面自组织成动态蛋白组装体，从而导致膜融合。该工艺不需要GTP水解。令人惊讶的是，我们有证据表明DynA可能与噬菌体抗性有关。因此，与脊椎动物中相关的Mx蛋白类似，细菌动力蛋白可能是细菌先天免疫系统对抗病毒感染的一部分。我们将研究DynA如何通过有序复合体的形成介导膜融合，以及该复合体在膜融合后如何被分解。我们将进一步阐明细菌动力蛋白在细胞中的作用。

Proteins and lipids are heterogeneously distributed in biological membranes. Correct function of membrane proteins often depends on spatio-temporal organization into defined membrane areas. However, the lateral organization of the bacterial cell membrane has not been analyzed in detail and the influence on cellular processes such as cytokinesis and development remains largely unknown. We have already identified a bacterial flotillin that resides in membrane micro-domains and may contribute to lateral membrane organisation. Flotillins are raft marker proteins which are extensively modified on posttranslational level. These proteins assemble into oligomeric complexes which likely regulates their function. Using the anisotropic dye Laurdan, we have been able to show that bacterial flotillins directly influence membrane order, likely by preventing coalescence of liquid ordered regions. We will analyse how bacterial flotillin homologues in Bacillus subtilis are able to mediate spatial membrane organization and how this impacts function of membrane integral protein machineries such as the secretion system. In addition we have identified a bacterial dynamin-like protein, DynA that binds in a nucleotide-independent manner to negatively charged phospholipids. DynA is involved in membrane tethering and fusion. DynA localizes to septa and may contribute to efficient septum closure. DynA self-organizes into dynamic protein assemblies on membrane surfaces, thereby leading to membrane fusion. This process does not need GTP hydrolysis. Amazingly, we have evidence that DynA may be involved in phage resistance. Hence, similar to the related Mx proteins in vertebrates, bacterial dynamins could be part of a bacterial innate immune system against viral infection. We will study how DynA mediates membrane fusion by ordered complex formation and how this complex is disassembled after membrane fusion. Further we will clarify the cellular role of bacterial dynamins.