Degradation of atrazine utilizing triazine hydrolase (TrzN) from Arthrobacter aurescens TC1
Triazine hydrolase (TrzN) from Arthrobacter aurescens TC1 is a Zn(II) dependent hydrolytic dehalogenase from the amidohydrolase super family. TrzN has 22 unique substrates. Most notably, TrzN can hydrolytically dechlorinate atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) to its less toxic derivative hydroxyatrazine. Atrazine is a widely used synthetic herbicide which has an extensive list of potential environmental and health concerns. TrzN is a prime target for use in the engineering of biocatalysts for atrazine remediation. However, its catalytic and biochemical properties are not fully understood. This research project provides insight into the catalytic mechanism of TrzN as well as explores the enzymes use in biomaterials for atrazine degradation. Insight into the catalytic mechanism of TrzN has been provided in chapter 2. Three amino acids (Thr325, Glu241, and His274) showed significant catalytic importance. Thr325 is essential for catalysis and data agreed that an essential bond is formed between the Thr325 oxygen and the Zn(II)-bound water moiety which likely stabilizes the water moiety for nucleophilic attack. The mechanism functions based on a two proton transfer system. First the His274 residue removes a proton form the Zn(II)-bound water moiety. The proton is shuttle from His274 to Glu241 which can then form a hydrogen bond with the triazole nitrogen on the atrazine ring positioning it for nucleophilic attack. In chapters 3 and 4, TrzN was immobilized in alginate, sol-gel, and mesoporous nanoparticle (MSN) biomaterials. All of the biomaterials were catalytically active and could degrade atrazine to hydroxyatrazine. Using enzymes as biocatalyst can traditionally be tricky, the inability to recover the catalyst and the enzymes inherent unstable nature makes the process costly and inefficient. Often, the solution to these short comings has been to immobilize enzymes in functional biomaterials. The biomaterials tested in these chapters were all able to be recovered and reused cyclically and over several weeks while maintaining or improving TrzN’s stability. This research herein provides insight into a new avenue to design bioremediation methodologies for the removal of atrazine utilizing TrzN.
atrazine, biomaterials, bioremediation, metalloenzyme
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