Post‐translational Modification in Microviridin Biosynthesis

Abstract

Cyanobacteria are prolific producers of bioactive natural products that mostly belong to the nonribosomal peptide and polyketide classes. We show here how a linear precursor peptide of microviridin K, a new member of the microviridin class of peptidase inhibitors, is processed to become the mature tricyclic peptidase inhibitor. The microviridin (mvd) biosynthetic gene cluster of P. agardhii comprises six genes encoding microviridin K, an apparently unexpressed second microviridin, two RimK homologues, an acetyltransferase, and an ABC transporter. We have over-expressed three enzymes of this pathway and have demonstrated their biochemical function in vitro through chemical degradation and mass spectrometry. We show that a prepeptide undergoes post-translational modification through cross-linking by ester and amide bond formation by the RimK homologues MvdD and MvdC, respectively. In silico analysis of the mvd gene cluster suggests the potential for widespread occurrence of microviridin-like compounds in a broad range of bacteria.

Putative Antiparasite Defensive System Involving Ribosomal and Nonribosomal Oligopeptides in Cyanobacteria of the Genus Planktothrix

“…Planktothrix may therefore resist chytrids by relying on the combined action of multiple factors. Here it is important to keep in mind that while microcystins and anabaenopeptins are nonribosomal peptides (14), microviridins are produced through posttranslational modification of ribosomally synthesized precursor peptides (15). Planktothrix may therefore control chytrid infection by employing oligopeptides that are produced via very different biosynthetic pathways.…”

“…In addition, smaller amounts of cyanopeptolins and aeruginosins can be found (25,28). The genetic manipulation of NIVA-CYA126/8 and the resulting mutants with knockout mutations for microcystins (NIVA-CYA126/8 McyϪ), anabaenopeptins (NIVA-CYA126/8 ApnϪ), and microviridin K (NIVA-CYA126/8 MvdϪ) were described earlier (14,15,25). Briefly, mutants were obtained by electroporation of NIVA-CYA126/8 with a mutant version of one of the peptide synthesis genes, including recombinative replacement of the wild-type copy of this gene.…”

“…Of the several hundreds of compounds described to date, many can be assigned to a few major structural classes, including the anabaenopeptins, the microcystins, and the microviridins. Cyanobacterial strains often contain several oligopeptide classes at the same time, all formed separately by nonribosomal peptide synthetases (14) or through posttranslational modification of ribosomally synthesized precursor peptides (15). Multiple variants of a class may occur if a peptide synthetase exhibits relaxed substrate specificity.…”

“…We used a simple but unique experimental setup that employed the bloom-forming cyanobacterium NIVA-CYA126/8 as a host model. NIVA-CYA126/8 is the first example of a cyanobacterium with a reasonably complex secondary metabolism for which knockout mutants for all of its major oligopeptide classes exist (14,15,25). These mutants differ from the wild type by their inability to produce microcystins, anabaenopeptins, or microviridins only, and so comparing the mutants with their wild type is one of the most direct ways to identify the significance of certain oligopeptide classes to biotic interactions.…”

Proteomic analysis of post translational modifications in cyanobacteria

“…In cyanobacteria, only a few protein N-terminal acetylation events have been reported, for example, N-terminal acetylation of several proteins such as the Rieske iron-sulfur protein (PetC), Cytochrome b559 subunit beta (psbF) and Photosystem II reaction center protein J (psbJ) [39,74]. N-terminal acetylation of some cyanobacterial peptides [75] or toxins were also reported [76,77].…”