Abstract:Azoreductase is an FMN-dependent and NADH-dependent enzyme of Escherichia coli. This enzyme is responsible for the degradation of azo dyes. In this study, we retrieved the crystal structure of the enzyme from PDB and 18 azo dyes from NCBI PubChem compound. These azo dyes were then docked with the FMN-dependent NADH-azoreductase enzyme to analyze the binding affinity of the azo dyes with the enzymes and predict the catalytic sites. In this approach, we identified the catalytic residues of FMN-dependent and NADH dependent enzyme of Escherichia coli which were then evaluated in terms of properties including function, conservation, hydrogen bonding, B-factor and flexibility. The results indicated that Phe-172, Glu-174, Lys-145, Asp-146 and Lys-169 played an important role as catalytic site residues in the enzyme. It is hoped that this information will provide a better understanding of enzyme mechanisms and also be used to improve the designing strategies for dyes detoxification. In this study, the approach emphasizes on a better understanding of the biodegradation of some of the commercially important azodyes mediated by azoreductase from E. coli. Furthermore, the catalytic site residues information is essential for understanding and altering the substrate specificity and for the design of a harmless azodye.
Taxus wallichiana, an indigenous plant of North East India contains bioactive compounds such as Tamoxifen citrate and taxol (paclitaxel and docetaxel) which inhibit the growth of cancerous cells. Tamoxifen citrate in its active form competitively inhibits the binding of estradiol or estrogen with estrogen receptor and results in tumor suppression whereas the taxol compounds stabilize the tubulin protein in microtubules and inhibit cell division in cancerous cells. In this approach, important domains and motifs of the protein receptors were studied and analyzed followed by homology modeling and its validation. Molecular docking studies were carried out via tubulin and estrogen receptor with paclitaxel, docetaxel, and endoxifen (an active form of tamoxifen citrate). Hence it was verified that tubulin and estrogen receptor contain binding sites for the bioactive compounds found in T. wallichiana and these bioactive compounds after binding with these receptors result in the prevention of the proliferation of the tumorous cells by stabilizing the microtubules and preventing the intake of steroidal hormones by cells respectively.
The initial critical step of reduction of azo bond during the metabolism of azo dyes is catalysed by a group of NADH and FAD dependant enzyme called azoreductases. Although several azoreductases have been identified from microorganisms and partially characterized, very little is known about the structural basis of the substrate specificity and the nature of catalysis. Azoreductase enzyme of Pseudomonas putida has a wider broad spectrum of substrate specificity and capable of degrading a wide variety of azo dyes. In the present study, the crystal structure of the enzyme from PDB and 10 azo dyes from NCBI PubChem compound were retrieved and their interactions were studied. These azo dyes were then docked with the FMN-dependent NADH-azoreductase enzyme to analyze the binding affinity of the azo dyes with the enzyme and predict the catalytic sites. Consequently, the catalytic residues of FMNdependent and NADH dependent enzyme were then analysed in terms of properties including function, hydrogen bonding and flexibility. The results suggest that Ala-114, Phe-172 and Glu-174 play a predominant role as catalytic site residues in the enzyme. Furthermore, the approach emphasis on predicting the active sites of this enzyme where substrates can bind in order to give a better understanding of the biodegradation of some of the commercially important azodyes mediated by azoreductase. These results will pave way for further increase in azoreductase activity and for better understanding of the dye degradation pathway.
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