|Title:||Untersuchungen zur Biosynthese und Funktion von Myxochelinen in Myxobakterien|
|Abstract:||The myxochelins were first mentioned in the literature nearly 30 years ago and described as catechol-type siderophores produced by myxobacteria. Since then, totally eight members of this compound class have been discovered, namely myxochelins A, B, C, D, as well as the structurally related hyalachelins A, B, C, and the recently isolated pseudochelin A. Current studies show that myxochelin biosynthesis is not restricted to myxobacteria, as assumed for a long time, but occurs in phylogenetically diverse bacterial groups. In the present thesis, a detailed analysis of the distribution of myxochelin biosynthesis was conducted. Myxochelin A is a potent inhibitor of the human 5-lipoxygenase (5-LOX), an enzyme involved in the biosynthesis of inflammatory mediators, i.e., the leukotrienes. Since the 5-LOX harbors a non-heme iron serving as redox mediator during catalysis, the question arose if the inhibition of this enzyme is due to the iron-binding capacity of myxochelin A. In order to gain more knowledge about the mode of action, 14 new structural analogues were generated using the precursor-directed biosynthesis approach and their biological activities were evaluated. Furthermore, the biosynthesis of pseudochelin A, a recently discovered myxochelin derivative, was elucidated. Bioinformatic analysis led to the identification of the enzyme, which is responsible for the production of pseudochelin A, namely MxcM, a putative member of the amidohydrolase superfamily. In vitro studies with recombinant enzyme confirmed that MxcM catalyzes the conversion of myxochelin B to pseudochelin A. Subsequently, the in vivo functionality of MxcM was evaluated using the myxobacterium Myxococcus xanthus. The heterologous expression was not based on chromosomal integration of the target gene. Instead a stable expression vector was designed and introduced into M. xanthus, a hitherto unprecedented procedure. Thus, two different expression strains were generated, which were able to produce pseudochelin A additionally to myxochelin A and B. Except for their biosynthesis, the question concerning the biological role of myxochelins was addressed as well. Although it is generally accepted that they act as siderophores, some natural myxochelin derivatives were found to possess rather low iron affinities. In this context several theories about further biological functions of the myxochelins have been discussed, e.g. as regulators of the lipoxygenase activities or as signal molecules involved in intercellular communication of the myxobacteria. In order to test a direct influence of the myxochelins on the morphology, the growth or the development of multicellular swarms of myxobacteria, a M. xanthus mutant strain harboring a disturbed myxochelin biosynthesis pathway was created. Interestingly, the mutant strain was not showing any growth defects, but the morphology of its swarm was significantly altered compared to the wildtype strain.|
|Subject Headings (RSWK):||Siderophore|
|Appears in Collections:||Lehrstuhl Technische Biologie|
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