The solution NMR structure of a blue-green algae hepatotoxin, microcystin-RR - A comparison with the structure of microcystin-LR

The microcystin-RR structures are compared with the structures of microcystin-LR in solution as well as in the crystal structure of the complex with protein phosphatase. The gross structures of the two peptides are similar, but with a more accentuated and compact saddle structure for microcystin-RR. The structural differences affect the hydrogen-bond pattern in the peptides and the location of the side chain of N-methyldehydroalanine, both of which are important for the ability of the peptide to form a tight complex with protein phosphatase. These structural differences may contribute to the observed differences in toxicity of microcystin-RR and microcystin-LR.