Genome Mining, Isolation and Characterization of Novel Lasso Peptides and Their Utilization in Drug Development

Lasso peptides are a class of natural products that belong to the family of ribosomally‑assembled and posttranslationally‑modified peptides. They are defined by an unique structural motif referred to as the so‑called lariat knot, whose name is derived from the fact that this topology is reminiscent of the knot found in the noose of a lasso. This structure is achieved by the presence of an N‑terminal macrolactam ring that is threaded by the C‑terminal tail of the peptide. The fold in these molecules is then conserved by non‑covalent interactions in the form of bulky amino acids located above and below the macrolactam ring, in this way entrapping the tail inside of the ring. What makes these compounds of interest for research is that their structure, even though it is maintained merely by sterical interactions, often exhibits a tremendous stability against thermal, chemical and proteolytic degradation. Still, up to now little is known about the general function of these compounds for their producing organisms, although there are some interesting biological activities attributed to some of the previously reported lasso peptides. To obtain more information about their physico‑chemical properties, their biosynthesis and to get an idea what role they might play in nature, the primary subject of this thesis was the directed genome mining for and the subsequent isolation and characterization of novel lasso peptides. The results of these projects were published in several studies that will be shown and discussed in the course of this thesis. Amongst other findings, these studies not only include the discovery of a multitude of novel lasso peptides, but through the thorough analysis and characterization of these compounds, several former assumptions of this research area could be overhauled and updated. In addition to this, the bioinformatic data gathered during our genome mining studies furthermore uncovered interesting facts about the distribution of lasso peptides amongst bacteria and about the existence of different subgroups of biosynthetic gene cluster arrangements, which could facilitate future research directed towards identifiying the concrete functions of these compounds. Furthermore, it was also investigated if these compounds are suitable scaffolds for drug development via epitope grafting approaches. In this regard, a previously reported bioactive lasso graft was used as the basis to show that such compounds can indeed be further optimized and improved upon by rational approaches that utilize the information obtained from research done with simple linear or cyclic peptides that are, in contrast to lasso peptides, easily accessible by synthetic means