Atrazine chlorohydrolase

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Bacterial degradation determines the environmental impact and efficacy of an herbicide or pesticide. Initially, most pesticides are highly effective and show minimal bacterial degradation; however, bacteria can rapidly evolve and gain the ability to metabolize potential nutrients in the environment. Despite a remarkable structural similarity, degradation of atrazine by bacteria capable of melamine degradation was rare; however, since its introduction as a pesticide in the United States, bacteria capable of atrazine degradation have evolved[1]. Currently, Pseudomonas sp. strain ADP seems to be the optimal bacterial strain for atrazine degradations, which appears to be the sole nitrogen source for the bacteria[2].

1 Reaction
2 Genetics
3 Specificity
4 References

[edit] Reaction

Atrazine Chlorohydrolase (AtzA) is an enzyme (E.C.3.8.1.8)[3], which catalyzes the conversion of atrazine to hydroxyatrazine. AtzA is an atrazine-dechlorinating enzyme with fairly restricted substrate specificity and plays a main role in the hydrolysis of atrazine to hydroxyatrazine in soils and groundwater[4]. Atrazine Hydroxyatrazine is a hydrolase (an enzyme that catalyzes the hydrolysis of a chemical bond ), which acts on halide bonds in C-halide compounds[5]. In 1993, pseudomonas sp. strain ADP was shown to degrade atrazine to cyanuric acid via three steps, the first of which is a dechlorination[6].

[edit] Genetics

De Souza, Sadowsky and Wackett were able to determine the nucleotide and amino acid sequence in 1996[7]. This enzyme is 98% identical in amino acid sequence, and subsequently in 3-D structure, to melamine deaminase but functionally different catalyzing the degradation of different substrates[8]. The gene coding for the enzyme shows 99% similarity between bacteria[9]. In fact there is only a 9-nucleotide difference, directly corresponding to the amino acid differences[10]. The nucleotide differences are unlikely to cause a conformational change in the enzyme but rather site-specific alterations[11]. This seems logical considering the remarkable similarity in the substrates and the relatively short period of evolution.

[edit] Specificity

AtzA was shown to displace fluoride as well as chlorine but not azido, cyano, methoxy, which are of similar size and electronegativity, or thiomethyl or amino groups[12]. The inability of AtzA to perform deamination makes it unique within its superfamily, amidohydrolases[13]. Furthermore, atrazine is not degraded by melamine deaminase and it does not inhibit melamine deaminase activity suggesting the active site is not specific for atrazine [14].