Conformational Studies of Microcystin-LR Using NMR Spectroscopy and Molecular Dynamics Calculations^,

Abstract

NMR spectroscopy in aqueous and dimethyl sulfoxide/water solutions is used to determine the three-dimensional structures of microcystin-LR, a cyclic cyanobacterial heptapeptide toxin which is a potent inhibitor of type 1 and type 2A protein phosphatases. The conformations of this toxic peptide are studied using a simulated annealing (SA) protocol followed by refined SA calculations in vacuo and free MD simulations in water. Only one conformational family in each solvent is found. The peptide ring has a saddle-shaped form, essentially the same in both solvents. The structural difference observed between the two solution structures is located to the part consisting of Mdha, Ala, and Leu. This peptide segment is not present in nodularin, a cyclic pentapeptide of similar toxicity. The Arg side chain is very flexible, while the side chain of Leu is well defined. The side chain of Adda, essential for toxicity, is constrained in the vicinity of the backbone ring but appears to be flexible in the more remote part.

A Molecular Basis for Different Interactions of Marine Toxins with Protein Phosphatase-1

“…The structure of microcystin-LY in dimethyl sulfoxide was described as being a boat-like ring with the Adda residue protruding form the concave side, which is more in line with our microcystin-LR and microcystin-LL structures. Recently, a paper was published comparing the structure of microcystin-LR in water and in dimethyl sulfoxide (30). In this study, microcystin-LR was found to have the same structure in water and dimethyl sulfoxide, and both structures were similar to our previously published free solution structure (1).…”

Production and specificity of mono and polyclonal antibodies against microcystins conjugated through N-methyldehydroalanine

“…In support of this assumption, it has been reported that MC derivatives, in which Adda is destroyed by ozonolysis, are not immunoreactive (Chu et al, 1989). Furthermore, three-dimensional NMRbased structure analysis of MCs (Trogen et al, 1996) and nodularin showed that Adda is the best-exposed part of both peptides. Adda will also be one of the best exposed parts of the MC molecule in conjugates produced both by conjugation through carboxy-groups or by conjugation through an introduced amino group.…”

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) from a large shallow, eutrophic lake of the subtropical China

“…MCs have the general structure cyclo-(D-Ala-L-X-erythro-b-methyl-D-isoAsp-L-Y-Adda-D-isoGlu-N-Methyldehydro-Ala), where Adda refers to the b-amino acid residue of 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-deca-4,6-idenoic acid, and X and Y represent variable L-amino acids (Carmichael, 1992;Dawson, 1998). The unusual amino acid Adda is essential for expression of biological activity (Trogen et al, 1996). Until now, more than 60 structurally different microcystins have been identified (Carmichael, 1994;Dawson, 1998).…”