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The structure of the hexameric atrazine chlorohydrolase AtzA.

Peat TS, Newman J, Balotra S, Lucent D, Warden AC, Scott C - Acta Crystallogr. D Biol. Crystallogr. (2015)

Bottom Line: Atrazine chlorohydrolase (AtzA) was discovered and purified in the early 1990s from soil that had been exposed to the widely used herbicide atrazine.It was subsequently found that this enzyme catalyzes the first and necessary step in the breakdown of atrazine by the soil organism Pseudomonas sp. strain ADP.Although it has taken 20 years, a crystal structure of the full hexameric form of AtzA has now been obtained.

View Article: PubMed Central - HTML - PubMed

Affiliation: CSIRO Biomedical Manufacturing, Parkville, Australia.

ABSTRACT
Atrazine chlorohydrolase (AtzA) was discovered and purified in the early 1990s from soil that had been exposed to the widely used herbicide atrazine. It was subsequently found that this enzyme catalyzes the first and necessary step in the breakdown of atrazine by the soil organism Pseudomonas sp. strain ADP. Although it has taken 20 years, a crystal structure of the full hexameric form of AtzA has now been obtained. AtzA is less well adapted to its physiological role (i.e. atrazine dechlorination) than the alternative metal-dependent atrazine chlorohydrolase (TrzN), with a substrate-binding pocket that is under considerable strain and for which the substrate is a poor fit.

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Plausible reaction mechanisms for AtzA. Two plausible reaction mechanisms are proposed involving either bidentate (a) or mondentate (b) coordination of the atrazine Cl atom to the Fe2+ centre of the AtzA active site.
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fig8: Plausible reaction mechanisms for AtzA. Two plausible reaction mechanisms are proposed involving either bidentate (a) or mondentate (b) coordination of the atrazine Cl atom to the Fe2+ centre of the AtzA active site.

Mentions: We present two alternative potential catalytic mechanisms for the hydrolytic dechlorination of atrazine by AtzA that are constant with the in silico docking presented here, notwithstanding that empirical data will be required to test these and previously proposed reaction mechanisms. The first is based directly upon the interactions shown in the only docking pose that oriented atrazine appropriately for nucleophilic attack and the second is based upon the abovementioned monodentate coordination mode for atrazine (Figs. 8 ▶a and 8 ▶b, respectively) that better enables Glu246 to stabilize negative charge on another of the ring N atoms. In both of these mechanisms, coordination of the Cl atom to Fe2+ draws electron density from the C—Cl bond, increasing the susceptibility of the C atom to nucleophilic attack. In the first mechanism, the coordinated water is deprotonated by Asp327 followed by nucleophilic attack of the resulting activated hydroxide at the chlorine-bearing ring C atom. The negative charge of the tetrahedral intermediate is stabilized on the Fe2+-coordinated aromatic N atom, after which chloride is released and aromaticity is re-established in the hydroxylated product.


The structure of the hexameric atrazine chlorohydrolase AtzA.

Peat TS, Newman J, Balotra S, Lucent D, Warden AC, Scott C - Acta Crystallogr. D Biol. Crystallogr. (2015)

Plausible reaction mechanisms for AtzA. Two plausible reaction mechanisms are proposed involving either bidentate (a) or mondentate (b) coordination of the atrazine Cl atom to the Fe2+ centre of the AtzA active site.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4356373&req=5

fig8: Plausible reaction mechanisms for AtzA. Two plausible reaction mechanisms are proposed involving either bidentate (a) or mondentate (b) coordination of the atrazine Cl atom to the Fe2+ centre of the AtzA active site.
Mentions: We present two alternative potential catalytic mechanisms for the hydrolytic dechlorination of atrazine by AtzA that are constant with the in silico docking presented here, notwithstanding that empirical data will be required to test these and previously proposed reaction mechanisms. The first is based directly upon the interactions shown in the only docking pose that oriented atrazine appropriately for nucleophilic attack and the second is based upon the abovementioned monodentate coordination mode for atrazine (Figs. 8 ▶a and 8 ▶b, respectively) that better enables Glu246 to stabilize negative charge on another of the ring N atoms. In both of these mechanisms, coordination of the Cl atom to Fe2+ draws electron density from the C—Cl bond, increasing the susceptibility of the C atom to nucleophilic attack. In the first mechanism, the coordinated water is deprotonated by Asp327 followed by nucleophilic attack of the resulting activated hydroxide at the chlorine-bearing ring C atom. The negative charge of the tetrahedral intermediate is stabilized on the Fe2+-coordinated aromatic N atom, after which chloride is released and aromaticity is re-established in the hydroxylated product.

Bottom Line: Atrazine chlorohydrolase (AtzA) was discovered and purified in the early 1990s from soil that had been exposed to the widely used herbicide atrazine.It was subsequently found that this enzyme catalyzes the first and necessary step in the breakdown of atrazine by the soil organism Pseudomonas sp. strain ADP.Although it has taken 20 years, a crystal structure of the full hexameric form of AtzA has now been obtained.

View Article: PubMed Central - HTML - PubMed

Affiliation: CSIRO Biomedical Manufacturing, Parkville, Australia.

ABSTRACT
Atrazine chlorohydrolase (AtzA) was discovered and purified in the early 1990s from soil that had been exposed to the widely used herbicide atrazine. It was subsequently found that this enzyme catalyzes the first and necessary step in the breakdown of atrazine by the soil organism Pseudomonas sp. strain ADP. Although it has taken 20 years, a crystal structure of the full hexameric form of AtzA has now been obtained. AtzA is less well adapted to its physiological role (i.e. atrazine dechlorination) than the alternative metal-dependent atrazine chlorohydrolase (TrzN), with a substrate-binding pocket that is under considerable strain and for which the substrate is a poor fit.

Show MeSH
Related in: MedlinePlus