Cyanopeptolins, new depsipeptides from the cyanobacterium Microcystis sp. pcc 7806.

Abstract

L-Threonine is connected to L-valine via its hydroxy-group forming an ester bonding. The hexanoic acid residue is attached to the TV-terminal aspartic acid residue which is not a part of the ring structure. The isolation procedure of the four cyanopeptolins as well as structure elucidation are described. Amino acid analysis, GC/MSanalysis, FAB-MSand several NMRtechniques were used to reveal the structures.Cyanobacteria (blue green algae) commonly found in fresh and brackish waters are well known to produce a manifold spectrum of secondary metabolites belonging to different substance classes such as alkaloids, phenolic dilactones, polyketides, amides, sulfur compounds, macrolides and peptides1}. Their most abundant peptide metabolites are cyclic peptide hepatotoxins termed microcystins. They are produced by strains of several waterbloom-forming cyanobacteria mainly from the genus Microcystis and are responsible for worldwide animal poisoning. Besides these well investigated toxins little is knownabout other peptides or peptide-related compounds produced by cyanobacteria. The tricyclic depsipeptide microviridin consisting of 14 L-amino acids has been found in Microcystis viridis from a lake in Japan. The depsipeptide acts as a strong inhibitor of thyrosinase2). Majusculamide C, a cyclic depsipeptide that inhibits the growth of a number of fungal plant pathogens has been isolated from Lyngbya majuscula3). The cyanobacterium Anabaena sp. BQ-16-1 produces a chlorine-containing cyclic decapeptide named puwainaphycin C which shows cardioactivity4).Recently, a fungicidal decapeptide named calophycin has been isolated from Calothrixfusca5\ and a cytotoxic bistratamide-related cyclic peptide, called westiellamide, was identified in the terrestrial cyanobacterium Westiellopsis prolifera6\ From Microcystis sp. PCC7806, f W.

Insertional mutagenesis of a peptide synthetase gene that is responsible for hepatotoxin production in the cyanobacterium Microcystis aeruginosa PCC 7806

“…It was found to contain mainly MCYST-LR, (D-Asp 3 )MCYST-LR and cyanopeptolin depsipeptides (Martin et al, 1993). The strain showed comparably fast growth rates on 1% agar plates.…”

“…Other microcystins, identified as minor components, were also not detected. The molecular ion peak at m/z 957 represents cyanopeptolin A and D (Martin et al, 1993) and was conserved in both wild-type and mutant cell line extracts. An additional peak in both cell lines at m/z 939.5 was tentatively identified as a dehydrated fragment of m/z 957 (data not shown).…”

“…(Moore et al, 1991). L-phenylalanine, a precursor for the Adda moiety of microcystin, and L-arginine are necessary for both microcystins and cyanopeptolins of Microcystis, whereas L-valine is found in cyanopeptolins and not microcystins (Martin et al, 1993). The in vitro inhibition of eukaryotic PP-1 and 2A is a direct indication of microcystin toxicity and was used to demonstrate the loss of microcystin bioactivity in the mutant Microcystis cell line.…”

“…A number of non-microcystin peptides, possibly formed via non-ribosomal peptide synthesis, such as the microcystins, have also been found in Microcystis and other bloom-forming cyanobacteria (Kaya, 1996). The group of Ahp (3-amino-6-hydroxy-2-oxo-1-piperidine) containing depsipeptides appears to be as abundant as the hepatotoxins (Martin et al, 1993). The possibility of protein phosphatase inhibition, and hence hepatotoxicity, by other cellular products of cyanobacteria has also not been determined.…”

Production of Secondary Metabolites by Freshwater Cyanobacteria

“…3). 4) This was the first time that bioactive peptides other than microcystins were isolated from toxic freshwater cyanobacteria. Since then it has been recognized that cyanobacteria produce not only toxins but also other type-compounds.…”