These interactions altogether brings the carbonyl oxygen atom of N-terminal peptide bond close to the catalytic metal ion. A pcation interaction was formed between the side chain of Cterminal Arg residue and Y378, which was found highly fluctuating in rmsf analysis. This p-cation interaction between the same atoms was observed in R563A and K565A systems as well whereas it was between Y383 and C-terminal Arg residue in E271Q system (Figure 8 ). The binding mode of the substrate in E271Q system was different to that of WT system. The strength of the hydrogen bonds with R563 and K565 has become weak in this system because of the conformational changes of both carboxylate of substrate and R565 residue ( Figure 8B ). The metal ion located in the active center was thrown away from its initial position because of the absence of negatively charged E271. This behavior observed in this system clearly reveals that E271 acts as a hook to hold the Zn 2+ ion in the active site. In terms of R563A system, the observed binding mode of this system is similar to that of E271Q system ( Figure 8C ). The metal ion was hooked by the presence of E271 residue but still the distance between Zn 2+ and the carbonyl oxygen atom of N-terminal peptide bond was high compared to that of WT. The hydrogen bonds were formed between Y378, Y383, and G269 residues. Surprisingly, two hydrogen bonds were formed with K565 residue in absence of R563. This is different compared to that of the equivalent L-LTA4 system where the hydrogen bonds with both the positively charge residues were completely lost. This observation indicates the importance of K565 in assisting R563 in carboxylate recognition during peptide binding. In K565A system, the binding mode of the substrate is folded and completely different to the other systems. The hydrogen bonds were observed only with Y383 and A565 residues along with an additional p-s interaction between Y378 and C- terminal Arg residue ( Figure 8D ). No hydrogen bonds were formed with R563 residue, which is one of the positively charged carboxylate recognition site residues. The molecular interactions observed in R563A and K565A systems revealed that both the residues are important for recognizing the carboxylate group and aligning the peptide substrate along the catalytic elements as reported.