possible, supplying pigments and power by means of carbon fixation, and inside the defense mechanism by the production of secondary metabolites. Published reports have demonstrated that as a consequence of these processes, cyanobacteria have their metabolic profile altered, resulting within the production of distinct variants of organic products. The compound 2-(2′,4′-dibromophenyl)-4,6-dibromophenol is solely biosynthesized by a cyanobacterium belonging to genus Oscillatoria in association together with the spongeToxins 2021, 13,19 ofDysidea herbacea [104]. These variables corroborate using the hypothesis that anabaenopeptins mainly observed in sponges could possibly be of cyanobacterial origin, as brominated APs variants had been isolated only from sponges [28,31,33] and also the Oscillatoria genus is known for APs production. For instance, the polyketide nosperin and a few variants of oligopeptide nostopeptolide are encountered exclusively throughout symbiosis, which may be exactly the same mechanism for anabaenopeptin variants production discovered in sponges. 4. Biosynthesis The attributes of Anabaenopeptins are connected to Non-Ribosomal Peptide Synthetases (NRPSs), which operate having a nucleic acid-free mechanism in the protein level and are structured as multifunctional proteins. NRPSs are organized as gene clusters in bacteria, normally possessing all of the proteins needed for suitable biosynthesis on the secondary metabolites, from the generation of creating blocks to solution transport [10507]. The variability of NRP structures, each cyclic and linear, reflects the idea from the complicated CDK3 review modular program of NRPSs organized as an assembly line. Every single module is responsible for the activation and coupling of an amino acid towards the respective oligopeptide being synthesized. The principle referred to as the collinearity rule dictates that, for example, a hexapeptide demands six modules to become made. Those modules are composed of enzymatic domains present in an NRPS, which are accountable for distinct MAO-B custom synthesis biosynthetic steps, as amino acid activation, bond formation, and oligopeptide liberation. In addition to the initiation module, an elongation module from an NRPS calls for, at least, an Adenylation-domain (A-domain) for amino acid recognition and activation; the Thiolation-domain (T-domain), required to carry the synthesized peptide; along with 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 proper maturation from the peptide, also responsible for the cyclization step [18,10508]. Comparable to other peptides developed by NRPS, the biosynthesis of APs requires all of the precise actions from the assembly line. Apart from, on account of some distinct qualities present within this cyclic hexapeptide and its variants, other proteins and domains also can 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]. Besides the fact that the anabaenopeptin structure’s initial 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 five genes (anaABCDE): four NRPSs, and an ATP-Binding Cassette-transporter (ABC-transporter) protein. It was also visualized NRPSs possessing an epimerase domain (AnaA) and a