Genetic analysis of the peptide synthetase
genes for a cyclic heptapeptide microcystin in Microcystis spp.
It was proposed that a polyketide synthase (PKS) catalyzes the condensation of a chlorobutanoyl intermediate with an acetate unit, and subsequently with the clyclohexenyl-alanine amino acid arising from the shikimate pathway which is incorporated into the product by the activity of a non-ribosomal peptide synthetase
Microcystin is a hepatotoxin produced by a non-ribosomal pathway through a polyketide synthase/non-ribosomal peptide synthetase
(PKS/NRPS) complex known as microcystin synthetase, which is responsible for the incorporation of amino acids in the peptide chain (Kleinkauf and von Dohren, 1996; Dittmann et al., 1997).
The BB and many of the siderophores are produced non-ribosomally by large, multi-domain enzymes termed as non-ribosomal peptide synthetases
(NRPS) that can assemble peptides of wide structural diversity and broad biological activity .