Structure and Function of Salmochelins and Microcins M/H47

对许多致病菌来说，铁的供应是一个关键因素，因为在它们的宿主中铁与蛋白质结合。在低铁生长条件下，大肠杆菌分泌一种铁载体（铁络合剂），称为肠杆菌素（肠切素）。特定的高亲和力运输系统允许铁肠杆菌蛋白的摄取，以提供生长所需的铁。自1970年以来，人们一直认为肠杆菌素是沙门氏菌菌株的主要铁载体。然而，我们最近发现，大多数沙门氏菌菌株分泌的主要铁载体是二糖基化肠杆菌素。salmochelin的合成和利用是由iroBCDEN基因编码的。在计划的项目中，将对新型碱切菌素及其降解产物的化学结构进行表征。此外，基因产物在生物合成、运输和降解中的功能和活性将通过化学和遗传方法进行研究和表征。由于肠obactin在哺乳动物体内与血清白蛋白紧密结合，在炎症中与NGAL脂钙蛋白紧密结合，宿主的这些先天防御机制似乎使肠obactin成为致病菌的低等铁载体。因此，salmochelins与白蛋白和NGAL脂钙蛋白的结合特性将被研究。该项目的第二部分集中在由几种产盐切菌素的大肠杆菌菌株分泌的微霉素H47和M上。这些微霉素能杀死多种不同的大肠杆菌菌株，并与盐切菌素和肠杆菌素一样，使用相同的儿茶酚酸铁载体受体。此外，在微霉素H47和微霉素M生物合成的基因簇中发现了iroB和iroD的同源基因mcmL和mcmK。随着这些微蛋白的结构的阐明，对McmL和McmK的修饰作用和微蛋白的功能进行了进一步的研究。

For many pathogenic bacteria iron supply is a critical factor since in their host iron is bound to proteins. Under low iron growth conditions E. coli secretes a siderophore (iron complexing agent) called enterobactin (enterochelin). Specific high affinity transport systems allow the uptake of iron-enterobactin in order to supply the iron necessary for growth. Since 1970 it has been assumed that enterobactin is a major siderophore of Salmonella strains. However, we recently showed that salmochelin, a diglucosylated enterobactin is the principal siderophore secreted by most Salmonella strains. Synthesis and utilization of salmochelin is encoded by the iroBCDEN genes. In the planned project, the chemical structures of novel salmochelins and its degradation products will be characterized. Furthermore, the functions and activities of the gene products in biosynthesis, transport and degradation will be studied and characterized with chemical and genetic methods. Since, enterobactin is avidly bound in the mammal by serum albumins and in inflammation by NGAL lipocalin, these innate defense mechanisms of the host seem to make enterobactin an inferior siderophore for pathogenic bacteria. Therefore, the binding properties of salmochelins to albumins and NGAL lipocalin will be examined. The second part of the project is focused on microcins H47 and M secreted by several salmochelin producing E. coli strains. These microcins kill a broad spectrum of different E. coli strains and use the same catecholate siderophore receptors as salmochelins and enterobactin. Furthermore, the genes mcmL and mcmK, which are homologs of iroB and iroD, are found in the gene cluster for microcin H47 and M biosynthesis. With the structure elucidation of these microcins conclusions are expected on the putative modification by McmL and McmK and on the function of microcins.