An orthogonal system for heterologous expression of actinobacterial lasso peptides in Streptomyces hosts

Lasso peptides are ribosomally synthesized and post-translationally modified peptides produced by bacteria. They are characterized by an unusual lariat-knot structure. Targeted genome scanning revealed a wide diversity of lasso peptides encoded in actinobacterial genomes, but cloning and heterologous expression of these clusters turned out to be problematic. To circumvent this, we developed an orthogonal expression system for heterologous production of actinobacterial lasso peptides in Streptomyces hosts based on a newly-identified regulatory circuit from Actinoalloteichus fjordicus. Six lasso peptide gene clusters, mainly originating from marine Actinobacteria, were chosen for proof-of-concept studies. By varying the Streptomyces expression hosts and a small set of culture conditions, three new lasso peptides were successfully produced and characterized by tandem MS. The newly developed expression system thus sets the stage to uncover and bioengineer the chemo-diversity of actinobacterial lasso peptides. Moreover, our data provide some considerations for future bioprospecting efforts for such peptides. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Cre- ative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not per- mitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ © The Author(s) 2018