US EPA

7416185 

Journal Article 

Computational study of the covalent bonding of microcystins to cysteine residues--a reaction involved in the inhibition of the PPP family of protein phosphatases 

Pereira, , SR; Vasconcelos, VM; Antunes, A; , 

2013 

1 

FEBS Journal
ISSN: 1742-464X
EISSN: 1742-4658 

WILEY 

HOBOKEN 

280 

2 

674-680 

English 

22177231 

10.1111/j.1742-4658.2011.08454.x 

WOS:000313906000024 

http://doi.wiley.com/10.1111/j.1742-4658.2011.08454.x
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Microcystins (MCs) are cyclic peptides, produced by cyanobacteria, that are hepatotoxic to mammals. The toxicity mechanism involves the potent inhibition of protein phosphatases, as the toxins bind the catalytic subunits of five enzymes of the phosphoprotein phosphatase (PPP) family of serine/threonine-specific phosphatases: Ppp1 (aka PP1), Ppp2 (aka PP2A), Ppp4, Ppp5 and Ppp6. The interaction with the proteins includes the formation of a covalent bond with a cysteine residue. Although this reaction seems to be accessory for the inhibition of PPP enzymes, it has been suggested to play an important part in the biological role of MCs and furthermore is involved in their nonenzymatic conjugation to glutathione. In this study, the molecular interaction of microcystins with their targeted PPP catalytic subunits is reviewed, including the relevance of the covalent bond for overall inhibition. The chemical reaction that leads to the formation of the covalent bond was evaluated in silico, both thermodynamically and kinetically, using quantum mechanical-based methods. As a result, it was confirmed to be a Michael-type addition, with simultaneous abstraction of the thiol hydrogen by a water molecule, transfer of hydrogen from the water to the α,β-unsaturated carbonyl group of the microcystin and addition of the sulfur to the β-carbon of the microcystin moiety. The calculated kinetics are in agreement with previous experimental results that had indicated the reaction to occur in a second step after a fast noncovalent interaction that inhibited the enzymes per se. 

computational study; covalent bond; microcystins; PPP family; protein phosphatases; alanine derivative; arginine; carbon; carbonyl derivative; cysteine; glutathione; hydrogen; microcystin; microcystin LR; n methyldehydroalanine; phosphoprotein phosphatase; phosphoprotein phosphatase 1; phosphoprotein phosphatase 2A; phosphoprotein phosphatase 3; phosphoprotein phosphatase 4; phosphoprotein phosphatase 5; phosphoprotein phosphatase 6; phosphoprotein phosphatase 7; phosphoprotein phosphatase catalytic subunit; sulfur; thiol; tyrosine; unclassified drug; water; article; chemical structure; computer model; covalent bond; crystal structure; density functional theory; enzyme active site; enzyme activity; enzyme inhibition; enzyme kinetics; enzyme substrate; IC 50; mathematical analysis; Michael addition; molecular interaction; priority journal; protein binding; protein function; protein protein interaction; protein targeting; proton transport; quantum mechanics; structure analysis; thermodynamics; Carcinogens; Catalytic Domain; Computer Graphics; Cysteine; Enzyme Inhibitors; Isoenzymes; Microcystins; Microcystis; Models, Molecular; Molecular Structure; Phosphoprotein Phosphatases; Protein Binding; User-Computer Interface; Cyanobacteria; Mammalia