Objectives: Eumycetoma is a tropical neglected infectious disease causing large tumorous lesions on mainly the extremities. The current treatment consists of a combination of antifungal therapy with azoles and surgery. In order to predict which azoles, have the highest binding capacity to their drug target, a homology model based on the CYP51 target was constructed and its validity was tested by docking some of the currently available triazoles along with a set of synthetic compounds. 

Methods: Madurella mycetomatis 14-α-sterol demethylase (MmCYP51) Protein sequence (GenBank: KXX80456.1), was built using comparative modelling method using the SWISS MODEL server facilities. The best model which chosen was Aspergillus fumigatus 14-α sterol demethylase (AfCYP51) with PDB ID; 4UYM, with sequence identity 66.09% and resolution of 2.55Å. Coordinates which are conserved between the target and the template are copied from the template to the model. Insertions and deletions are remodelled using a fragment library. Side chains are then rebuilt. The 3D superposition of the target protein and the template was carried out, and the RMSD for alignment was determined. The docking study was conducted with the docking module of molecular operating environment (MOE) software. The compounds 3D structures were built with Chem3D software then were transferred and saved into MOE database, the energy of each compound was minimized by MMFF94x force field. Protein 3D structures were protonated & energy minimized using MMFF94x force field. Finally, the 3D structures of the prepared proteins were saved as PDB file. A Gaussian Contact surface was drawn around the binding site. The receptor was verified as Receptor and the site as Ligand Atoms. The Placement method used was Triangle Matcher. The first scoring function was set to London dG and the refinement to force field. 

Results: The molecular docking provided evidence that fosravuconazole 1 is interacting with the enzyme in a way that permits the phosphate group forms potential hydrogen bonding, besides the nitrile and triazole moieties (Figures 1 & 2). 
Docking results of synthetic compound 2 which previously exhibited promising in vitro activity (IC50 =0.60 µM) against Madurella myceromatus showed a strong affinity towards CYP51 providing further evidence of the role of a nitrile group in forming hydrogen bonding with enzyme's residues in a similar fusion to the azoles, exist in this compound and forms a potential hydrogen bond with the enzyme's residues. It worth noting that eumycetoma is currently treated with itraconazole. 

Conclusion:The constructed protein target seems to provide certain predictive value and correlation with the in vitro data.  Fosravuconazole represents a promise for eumycetoma treatment; however, comprehensive researches is required to discover novel potent drugs.  

References: Altschul, S.F., Madden, T.L., Schäffer, A.A., Zhang, J., Zhang, Z., Miller, W. and Lipman, D.J., Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. Nucleic acids research, 25(17), .3389-3402, 1997.




Molecular docking based on construction of 4-a-sterol demethylase (CYP51) as an active site of Madurella mycetomatis by homology modelling