possible, supplying pigments and energy by way of carbon fixation, and inside the defense mechanism by the production of secondary metabolites. Published reports have demonstrated that as a consequence of those processes, cyanobacteria have their metabolic profile altered, resulting within the production of distinct variants of natural goods. The compound 2-(2′,4′-dibromophenyl)-4,6-dibromophenol is solely biosynthesized by a cyanobacterium belonging to genus Oscillatoria in association using the spongeToxins 2021, 13,19 ofDysidea herbacea [104]. These aspects corroborate with the hypothesis that anabaenopeptins primarily observed in sponges might be of cyanobacterial origin, as brominated APs variants have been isolated only from sponges [28,31,33] and also the Oscillatoria genus is known for APs production. For example, the polyketide nosperin and some variants of oligopeptide nostopeptolide are encountered exclusively throughout symbiosis, which might be precisely the same mechanism for anabaenopeptin variants production found in sponges. four. Biosynthesis The capabilities of Anabaenopeptins are associated to D5 Receptor Species Non-Ribosomal Peptide Synthetases (NRPSs), which operate with a nucleic acid-free mechanism in the protein level and are structured as multifunctional proteins. NRPSs are organized as gene clusters in bacteria, typically possessing all the proteins necessary for suitable biosynthesis in the secondary metabolites, from the generation of building blocks to product transport [10507]. The variability of NRP structures, each cyclic and linear, reflects the notion of the complicated modular technique of NRPSs organized as an assembly line. Each and every module is responsible for the activation and coupling of an amino acid towards the respective oligopeptide becoming synthesized. The principle referred to as the collinearity rule dictates that, for instance, a hexapeptide requires six modules to become made. These modules are composed of enzymatic domains present in an NRPS, that are accountable for precise biosynthetic methods, as amino acid activation, bond formation, and oligopeptide liberation. Besides the initiation module, an elongation module from an NRPS demands, at the very least, an Adenylation-domain (A-domain) for amino acid recognition and activation; the Thiolation-domain (T-domain), expected to carry the synthesized peptide; in Coccidia web addition to a Condensation-domain (C-domain), responsible for the peptide bond formation. The final module of this assembly line requires the Thioesterase-domain (Te-domain) for the correct maturation of the peptide, also accountable for the cyclization step [18,10508]. Related to other peptides produced by NRPS, the biosynthesis of APs demands all the distinct measures on the assembly line. In addition to, resulting from some certain characteristics present in this cyclic hexapeptide and its variants, other proteins and domains can also be associated to its synthesis, as the biosynthetic apparatus for homoamino acid production and domains for D-Lys formation (Epimerization-domain; E-domain) and N-methylation of certain residues (Methylation-domain; M-domain) [18,19,105,106,108,109]. In addition to the truth that the anabaenopeptin structure’s very first detection in cyanobacteria occurred in 1995 [20], its gene cluster was only described ten years later within a Planktothrix rubescens strain [18]. The gene cluster detected within this cyanobacterium comprised of 5 genes (anaABCDE): four NRPSs, and an ATP-Binding Cassette-transporter (ABC-transporter) protein. It was also visualized NRPSs possessing an epimerase domain (AnaA) and also a
