Simultaneous purification of nitrile hydratase and amidase of Alcaligenes sp. MTCC 10674

Novel biodegradation pathway of insecticide flonicamid mediated by an amidase and its unusual substrate spectrum

The insecticide flonicamid (FLO) and its main degradation intermediate 4-trifluoromethylnicotinamide (TFNA-AM) are hazardous to the environment and animals. Microbial transformation of FLO has been well studied, but no study has yet reported on TFNA-AM degradation by a microorganism. Here, Pseudomonas stutzeri CGMCC 22915 effectively degraded TFNA-AM to 5-trifluoromethylnicotinic acid (TFNA). P. stutzeri CGMCC 22915 degraded 60.0% of TFNA-AM (1154.44 μmol/L) within 6 h with a half-life of just 4.5 h. Moreover, P. stutzeri CGMCC 22915 significantly promoted TFNA-AM decomposition in surface water. The reaction was catalyzed by an amidase, PsAmiA. PsAmiA is encoded in a novel nitrile-converting enzyme gene cluster. The enzyme shared only 20-44% identities with previously characterized signature amidases. PsAmiA was successfully expressed in Escherichia coli and its enzymatic properties were investigated using TFNA-AM as the substrate. PsAmiA was more active toward amides without hydrophilic groups, and did not hydrolyze another amide metabolite of FLO, N-(4-trifluoromethylnicotinoyl)glycinamide (TFNG-AM), which is structurally very similar to TFNA-AM. Molecular docking of PsAmiA and TFNA-AM indicated that hydrophobic residues Leu148, Ala150, Ala195, Ile225, Trp341, Leu460, and Ile463 may affect its substrate spectrum. This study provides new insights of the environmental fate of FLO at the molecular level and the structure-function relationships of amidases.

Cloning, expression and biochemical characterization of a novel amidase from Thauera sinica K11

A novel amidase (TAM) was identified and cloned from the genome of Thauera sinica K11. The recombinant protein was purified to homogeneity by one-step affinity chromatography for up to 26.4-fold with a yield of 38.1%. Gel filtration chromatography and SDS-PAGE revealed that the enzyme was a tetramer with a subunit of approximately 37.5 kDa. The amidase exhibited the maximum acyl transfer activity at 45 °C and pH 7.0, and it was highly stable over a wide pH range of 6.0-11.0. Inhibition of enzyme activity was observed in the presence of metal ions, thiol reagents and organic solvents. TAM showed a broad substrate spectrum toward aliphatic, aromatic and heterocyclic amides. For linear aliphatic monoamides, the acyl transfer activity of TAM was decreased with the extension of the carbon chain length, and thus the highest activity of 228.2 U/mg was obtained when formamide was used as substrate. This distinct selectivity of amidase to linear aliphatic monoamides expanded the findings of signature amidases to substrate specificity.

Bioinformatics of a Novel Nitrile Hydratase Gene Cluster of the N2-Fixing Bacterium Microvirga flocculans CGMCC 1.16731 and Characterization of the Enzyme

Microvirga flocculans CGMCC 1.16731 can degrade many cyano group-containing neonicotinoid insecticides. Here, its genome was sequenced, and a novel nitrile hydratase gene cluster was discovered in a plasmid. The NHase gene cluster (pnhF) has gene structure β-subunit 1, α-subunit, and β-subunit 2, which is different from previously reported NHase gene structures. Phylogenetic analysis of α-subunits indicated that NHases containing the three subunit (β1αβ2) structure are independent from NHases containing two subunits (αβ). pnhF was successfully expressed in Escherichia coli, and the purified PnhF could convert the nitrile-containing insecticide flonicamid to N-(4-trifluoromethylnicotinoyl)glycinamide. The enzymatic properties of PnhF were investigated using flonicamid as a substrate. Homology models revealed that amino acid residue β1-Glu56 may strongly affect the catalytic activity of PnhF. This study expands our understanding of the structures and functions of NHases and the enzymatic mechanism of the environmental fate of flonicamid.

Enzymes immobilization onto magnetic nanoparticles to improve industrial and environmental applications

Enzymes as specific natural biocatalysts are present in all living organisms and they play a key role in the biochemical reactions inside, as outside the cell. Despite the wide range of environmental, medical, agricultural, and food applications, the high cost, non-reusability, and limited stability of soluble (non-immobilized) enzymes are considered barriers to their commercial application. Immobilization techniques are an effective strategy for solving problems associated with free enzymes in terms of improving the efficiency and stability of catalytic enzymes, as well as enhancing their separation and reusability in continuous industrial applications. Out of different supporting materials, magnetic nanoparticles are considered as the future trend for enzyme immobilization due to their exceptional properties regarding stabilization, easy recovery and reuse. Some recent techniques of enzyme immobilization on magnetic nanoparticles will be detailed hereafter in the chapter.