Cloning and functional characterization of nitrilase from Fusarium proliferatum AUF-2 for detoxification of nitriles.

A fungal nitrilase gene from Fusarium proliferatum AUF-2 was cloned through reverse transcription-PCR. The open reading frame consisted of 903 bp and potentially encoded a protein of 301 amino acid residues with a theoretical molecular mass of 33.0 kDa. The encoding gene was expressed in Escherichia coli strain BL21 and the recombinant protein with His6-tag was purified to electrophoretic homogeneity. The purified enzyme exhibited optimal activity in the range of 35-40 °C and pH 8.0. EDTA, Mg(2+), Zn(2+), Ca(2+), Fe(2+), Fe(3+) and Mn(2+) stimulated hydrolytic activity, whereas Cu(2+), Co(2+) and Ni(2+) had inhibitory effect on nitrilase activity. Ag(+) ions showed a strong inhibitory effect on the recombinant nitrilase activity. This nitrilase was specific towards aliphatic, heterocyclic and aromatic nitriles. The kinetic parameters V(max) and K(m) for benzonitrile substrate were determined to be 14.6 μmol/min/mg protein and 1.55 mM, respectively. Homology modelling and molecular docking studies provided an insight into the substrate specificity and the proposed catalytic triad for recombinant nitrilase consisted of Glu-54, Lys-133 and Cys-175. This is the first report on the cloning and heterologous expression of nitrilase from Fusarium proliferatum.