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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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Related in: MedlinePlus

Density found in the active site of AtzA. A composite OMIT map was generated using the CCP4 package and the figure shows the ‘extra’ density seen in the active site which may be owing to atrazine (top of the figure, blue mesh). The active-site iron is shown as an orange sphere, water is shown as a red sphere and several active-site residues are shown with associated density. The OMIT map was set to 1σ.
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fig5: Density found in the active site of AtzA. A composite OMIT map was generated using the CCP4 package and the figure shows the ‘extra’ density seen in the active site which may be owing to atrazine (top of the figure, blue mesh). The active-site iron is shown as an orange sphere, water is shown as a red sphere and several active-site residues are shown with associated density. The OMIT map was set to 1σ.

Mentions: There are a number of Ramachandran outliers associated with the active site, His66, His276, Glu298, Asp327 and Asn332, which all have good electron density (Fig. 5 ▶) and are unambiguously placed. His66, His276 and Asp327 bind the Fe2+ in the active site directly and introduce strain into the active site. Most of the other Ramachandran outliers are also in good electron density. The one exception is Glu251, which is in a region of weak electron density and is likely to be mobile in the protein. This mobile region sits over the substrate and may be mobile in order to allow substrate entry or exit. One other Ramachandran outlier, Thr368, is interesting as it is in the middle of a helix; the preceding residue, Ala367, which is also part of the helical structure, has its carbonyl hydrogen-bonded to another residue (Ile63) instead of being in line with the other carbonyls in the helix.


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)

Density found in the active site of AtzA. A composite OMIT map was generated using the CCP4 package and the figure shows the ‘extra’ density seen in the active site which may be owing to atrazine (top of the figure, blue mesh). The active-site iron is shown as an orange sphere, water is shown as a red sphere and several active-site residues are shown with associated density. The OMIT map was set to 1σ.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: Density found in the active site of AtzA. A composite OMIT map was generated using the CCP4 package and the figure shows the ‘extra’ density seen in the active site which may be owing to atrazine (top of the figure, blue mesh). The active-site iron is shown as an orange sphere, water is shown as a red sphere and several active-site residues are shown with associated density. The OMIT map was set to 1σ.
Mentions: There are a number of Ramachandran outliers associated with the active site, His66, His276, Glu298, Asp327 and Asn332, which all have good electron density (Fig. 5 ▶) and are unambiguously placed. His66, His276 and Asp327 bind the Fe2+ in the active site directly and introduce strain into the active site. Most of the other Ramachandran outliers are also in good electron density. The one exception is Glu251, which is in a region of weak electron density and is likely to be mobile in the protein. This mobile region sits over the substrate and may be mobile in order to allow substrate entry or exit. One other Ramachandran outlier, Thr368, is interesting as it is in the middle of a helix; the preceding residue, Ala367, which is also part of the helical structure, has its carbonyl hydrogen-bonded to another residue (Ile63) instead of being in line with the other carbonyls in the helix.

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