Genome Mining, Phylogenetic and Structural Analysis of Bacterial Nitrilases for the Biodegradation of Nitrile Compounds

Abstract Microbial nitrilases play vital role in biodegradation of nitrile-containing contaminants in pollutant and effluents treatments in chemical and textile industries as well as the biosynthesis of IAA from tryptophan in plants. However, the lack of structural information hinders the correlation of its activity and substrate specificity. Here, we have identified bacterial genomes for nitrilases bearing unassigned functions including hypothetical, uncharacterized, or putative role. The genomic annotations revealed four predicted nitrilases encoding genes as uncharacterized subgroup of the nitrilase superfamily. Further, the annotation of these nitrilases revealed relatedness with nitrilase hydratases and cyanoalanine hydratases. The characterization of motif analysis of these protein sequences, predicted a single motif of 20-28 aa, and glutamate (E), lysine (K) and cysteine (C) residues as a part of catalytic triad along with several active site residues. The structural analysis of the modeled nitrilases revealed geometrical and close conformation of α-helices and β-sheets arranged in a sandwich structure. The catalytic residues constituted the substrate binding pocket and exhibited the wide nitrile substrate spectra for both aromatic and aliphatic nitriles containing compounds. The aromatic amino acid residues Y159 in active site were predicted to show importance for substrate specificity. The substitution of non-aromatic alanine residue in place of Y159 completely disrupted the catalytic activity for indole-3-acetonitrile. The present study reports several uncharacterized nitrilases which have not been reported so far for their role in the biodegradation of pollutants, xenobiotics which could find applications in industries.