[D-Asp3]microcystin-LR

• Hepatotoxic

[D-Asp³]microcystin-LR is a variant of microcystin-LR isolated from Microcystis aeruginosa. In this analog, the D-erythro-β-methylaspartic acid (D-MeAsp) residue at position 3 is replaced with aspartic acid (Asp), hence the designation [D-Asp³]. This microcystin contains leucine (L) at position 2 and arginine (R) at position 4. Like other microcystins, [D-Asp³]microcystin-LR is a potent hepatotoxin.

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Cyanobacteria are photosynthetic prokaryotes commonly found in freshwater ecosystems. The increasingly frequent occurrence of cyanobacterial blooms in lakes and rivers is closely linked to climate change and human activities, particularly nutrient enrichment. Microcystins are a group of cyclic heptapeptide hepatotoxins produced by several cyanobacterial genera, most notably Microcystis. Structurally, all microcystins share a conserved cyclic heptapeptide core with the general structure: cyclo(-D-Ala¹-X²-D-MeAsp³-Y⁴-Adda⁵-D-Glu⁶-Mdha⁷-), where X and Y are variable L-amino acids. D-MeAsp refers to D-erythro-β-methylaspartic acid, and Mdha is N-methyldehydroalanine. Adda (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-deca-4,6-dienoic acid) is a unique β-amino acid essential for the toxicity of microcystins. Substitutions at positions 2 and 4 define at least 21 primary microcystin analogs, such as microcystin-LR, while modifications at other positions – including demethylation, oxidation, or amino acid substitutions – have led to the identification of over 90 microcystin variants to date. [D-Asp³]microcystin-LR is one such variant, in which the D-MeAsp at position 3 is replaced by aspartic acid.