Cyanobacteria MC-LR

Microcystin-LR (MC-LR) is a naturally occurring toxin produced by cyanobacteria. It is one of a large family of microcystins. It is considered the most toxic compound of this family.

Microcystins are small nonribosomal peptides. In Microcystis aeruginosa microcystin-LR is synthesized by proteins that encoded by a 55 kb microcystin-gene cluster (mcy) that contains 6 large (over 3 kb) genes that encode proteins with polyketide synthase activity, nonribosomal peptide synthase activity (mcyA-E and G) and 4 smaller genes (mcyF and H-J). These large proteins are made up of different protein domains, coined 'modules', that each have their own specific enzymatic function. Although the enzyme systems involved in the biosynthesis of microcystins is not identical among all cyanobacteria, there are large similarities and most of the essential enzymes are conserved.