Microcystins phosphatase-bound

The ability to identify and quantify cyanobacterial toxins in animal and human clinical material following (suspected) intoxications or illnesses associated with contact with toxic cyanobacteria is an increasing requirement. The recoveries of anatoxin-a from animal stomach material and of microcystins from sheep rumen contents are relatively straightforward. However, the recovery of microcystin from liver and tissue samples cannot be expected to be complete without the application of proteolytic digestion and extraction procedures. This is likely because microcystins bind covalently to a cysteine residue in protein phosphatase. Unless an effective procedure is applied for the extraction of covalently bound microcystins (and nodiilarins), then a negative result in analysis cannot be taken to indicate the absence of toxins in clinical specimens. Furthermore, any positive result may be an underestimate of the true amount of microcystin in the material and would only represent free toxin, not bound to the protein phosphatases. Optimized procedures for the extraction of bound microcystins and nodiilarins from organ and tissue samples are needed. 

Finally, microcystin LY has a significantly larger stalk due to the parallel array of the Adda and Tyr side chains in a hydrophobic collapse-type interaction. If the size of this hydrophobic finger in the enzyme-bound state is conditioned by the size of the binding cleft of the protein phosphatases, dismption of the hydrophobic interaction between the Adda and Tyr side-chain is required for binding. The resulting large... 

The authors would like to thank Hans-Jurgen Musiol for valuable discussions and Norbert Schaschke for his help in the preparation of the manuscript. The coordinates of the X-ray structure of microcystin bound to protein phosphatase-1 were retrieved from the Brookhaven database (IFJM.pdb). 

Bagu, J.R. et al., A molecular basis for different interactions of marine toxins with protein phosphatase-1— molecular models for bound motnporin, microcystins, okadaic acid, and calycnlin A, J Biol Chem 272, 5087, 1997. 

---