Identification of TTA codon containing genes in Frankia and exploration of the role of tRNA in regulating these genes

Production of Epoxyketone Peptide-Based Proteasome Inhibitors by Streptomyces sp. BRA-346: Regulation and Biosynthesis

Streptomyces sp. BRA-346 is an Actinobacteria isolated from the Brazilian endemic tunicate Euherdmania sp. We have reported that this strain produces epoxyketone peptides, as dihydroeponemycin (DHE) and structurally related analogs. This cocktail of epoxyketone peptides inhibits the proteasome chymotrypsin-like activity and shows high cytotoxicity to glioma cells. However, low yields and poor reproducibility of epoxyketone peptides production by BRA-346 under laboratory cultivation have limited the isolation of epoxyketone peptides for additional studies. Here, we evaluated several cultivation methods using different culture media and chemical elicitors to increase the repertoire of peptide epoxyketone production by this bacterium. Furthermore, BRA-346 genome was sequenced, revealing its broad genetic potential, which is mostly hidden under laboratory conditions. By using specific growth conditions, we were able to evidence different classes of secondary metabolites produced by BRA-346. In addition, by combining genome mining with untargeted metabolomics, we could link the metabolites produced by BRA-346 to its genetic capacity and potential regulators. A single biosynthetic gene cluster (BGC) was related to the production of the target epoxyketone peptides by BRA-346. The candidate BGC displays conserved biosynthetic enzymes with the reported eponemycin (EPN) and TMC-86A (TMC) BGCs. The core of the putative epoxyketone peptide BGC (ORFs A-L), in which ORF A is a LuxR-like transcription factor, was cloned into a heterologous host. The recombinant organism was capable to produce TMC and EPN natural products, along with the biosynthetic intermediates DH-TMC and DHE, and additional congeners. A phylogenetic analysis of the epn/tmc BGC revealed related BGCs in public databases. Most of them carry a proteasome beta-subunit, however, lacking an assigned specialized metabolite. The retrieved BGCs also display a diversity of regulatory genes and TTA codons, indicating tight regulation of this BGC at the transcription and translational levels. These results demonstrate the plasticity of the epn/tmc BGC of BRA-346 in producing epoxyketone peptides and the feasibility of their production in a heterologous host. This work also highlights the capacity of BRA-346 to tightly regulate its secondary metabolism and shed light on how to awake silent gene clusters of Streptomyces sp. BRA-346 to allow the production of pharmacologically important biosynthetic products.

Genomic Insights into Evolution of AdpA Family Master Regulators of Morphological Differentiation and Secondary Metabolism in Streptomyces

The AdpA protein from a streptomycin producer Streptomyces griseus is a founding member of the AdpA family of pleiotropic regulators, known to be ubiquitously present in streptomycetes. Functional genomic approaches revealed a huge number of AdpA targets, leading to the claim that the AdpA regulon is the largest one in bacteria. The expression of adpA is limited at the level of translation of the rare leucyl UUA codon. All known properties of AdpA regulators were discovered on a few streptomycete strains. There are open questions about the true abundance and diversity of AdpA across actinobacterial taxa (and beyond) and about the possible evolutionary forces that shape the AdpA orthologous group in Streptomyces. Here we show that, with respect to the TTA codon, streptomycete adpA is more diverse than has been previously thought, as the genes differ in presence/position of this codon. Reciprocal best hits to AdpA can be found in many actinobacterial orders, with a domain organization resembling that of the prototypical AdpA, but other configurations also exist. Diversifying positive selection was detected within the DNA-binding (AraC) domain in adpA of Streptomyces origin, most likely affecting residues enabling AdpA to recognize a degenerate operator. Sequence coding for putative glutamine amidotransferase (GATase-1) domain also shows signs of positive selection. The two-domain organization of AdpA most likely arose from a fusion of genes encoding separate GATase-1 and AraC domains. Indeed, we show that the AraC domain retains a biological function in the absence of the GATase-1 part. We suggest that acquisition of the regulatory role by TTA codon is a relatively recent event in the evolution of AdpA, which coincided with the rise of the Streptomycetales clade and, at present, is under relaxed selective constraints. Further experimental scrutiny of our findings is invited, which should provide new insights into the evolution and prospects for engineering of an AdpA-centered regulatory network.

The PARIGA server for real time filtering and analysis of reciprocal BLAST results

BLAST-based similarity searches are commonly used in several applications involving both nucleotide and protein sequences. These applications span from simple tasks such as mapping sequences over a database to more complex procedures as clustering or annotation processes. When the amount of analysed data increases, manual inspection of BLAST results become a tedious procedure. Tools for parsing or filtering BLAST results for different purposes are then required. We describe here PARIGA (http://resources.bioinformatica.crs4.it/pariga/), a server that enables users to perform all-against-all BLAST searches on two sets of sequences selected by the user. Moreover, since it stores the two BLAST output in a python-serialized-objects database, results can be filtered according to several parameters in real-time fashion, without re-running the process and avoiding additional programming efforts. Results can be interrogated by the user using logical operations, for example to retrieve cases where two queries match same targets, or when sequences from the two datasets are reciprocal best hits, or when a query matches a target in multiple regions. The Pariga web server is designed to be a helpful tool for managing the results of sequence similarity searches. The design and implementation of the server renders all operations very fast and easy to use.